In an effort for Tom Cruise (who was 20 during filming) to look more "teenage" in appearance, the producers put him through an unusual bit of physical training. Cruise worked out seven days a week, in order to lose ten pounds. Once that had been accomplished, he immediately ceased working out and ate extremely fatty foods in order to add a layer of baby fat. This is how he achieved that "fresh-faced" teenage look.

Curtis Armstrong, making his film debut, kept a journal during filming. On his early impression of Tom Cruise he wrote: "Tom's an interesting character. Can't really make him out. He would appear to be on the brink of a great career. But when it comes to doing things with him - socially or professionally - he's not terribly reliable. Always late, very casual with other people's time. But in spite of it all, it's difficult not to like him. Though it's early days, the rehearsing I've done with him has gone smoothly. No arrogance or selfishness there. Yet. We'll see."

The sunglasses Joel wears are the Ray-Ban Wayfarer model. Annual sales of Wayfarers were languishing as of 1983 but skyrocketed 2,000 percent after the movie's release. This film and The Blues Brothers (1980) have contributed to the popularity of the Wayfarers since.

The dance scene where Joel dances to "Old Time Rock N' Roll" was completely improvised. In the script Tom Cruise was simply instructed to "dance to rock music."

According to Tom Cruise, Paul Brickman was initially unsure of casting him: "Originally, Paul had seen Taps (1981) and said, 'This guy for Joel? This guy is a killer! Let him do Amityville III!' Somehow, my agent, without me knowing, arranged to have me just drop by the office to say hello. So I went in wearing a jean jacket, my tooth was chipped, my hair was greasy. I was pumped up and talking in an Oklahoma accent, 'Hey, how y'all doing?' Paul just sat there, looking at me." Cruise returned to Tulsa to finish filming The Outsiders (1983), but flew back to L.A. and auditioned again. "I walk in and see this stunningly gorgeous woman sitting there looking at me and I'm thinking, 'Oh my God,'" Cruise said. "Rebecca [De Mornay] had already been cast. They wanted to see the two of us together. I tested, and to make a short story long, we didn't test that well. Paul just believed in me."

Continuity

When Joel is the den talking to the college admissions guy Lana walks into the room and closes the door behind her. Her long, blond hair is swinging around in the upper right of the screen. But an instant later all her hair is tucked up into a black hat.

When Joel first takes daddy's Porsche out, he stalls it going out of the garage. When leaving the hotel though, you can see the backup lights flash indicating an automatic (80 percent of Porsche 928's were automatic), then when Lana gets her purse out of the car at the lake, she bumps it into neutral.

The last item that Guido sells back to Joel is the glass egg. When Vicki throws the egg from the back of the truck, she is standing next to the flower print couch, still in the truck. In the very next shot of Joel, the couch is now sitting on the lawn. When he then goes to catch the egg, he jumps on the couch and then over to the piano.

During the car chasing scene, the Porsche turns the corner revealing very obviously only one person inside it.

Lana approaches Joel and Miles outside of the hotel as they are standing by the car. Lana then says "let's talk in the car" and moves between Joel and Miles to get in, and the sound of the door closing behind her. In the next shot, Joel opens the driver's side door, gets in and closes the door. Then, Miles is already in the backseat, though with the sequence shown, he could have never gotten in the car.



Factual errors

On two occasions in the film, Joel's SAT scores were revealed to be 597 Verbal and 560 Math. SAT scores were rounded to the nearest ten starting in the early seventies, so Joel's scores should both have ended in zeros.

When Joel is raking leaves at the end of the movie, he pauses and takes a cigarette out of a pack of Marlboro Reds. The cigarette is all white - Marlboro Reds have brown filters.

The Chicago transit system did not run single-car trains on its underground routes in 1983.

During the "love making scene" on the CTA "El" train, the car is shown moving towards and away from the camera from several different angles. Some of these were done by reversing the film, indicated by the "white headlights" on the front of the train, moving away from the camera (not the correct direction of travel) or the opposite situation, the "red tail/classification" lights on the rear of the train moving towards the camera.

The CTA car that Joel and the Hooker had sex on was part of the Lake/Dan Ryan line. The Lake/Dan Ryan line never ran underground in a subway, yet there is a scene in which the CTA car was in a subway.



Incorrectly regarded as goofs

Guido charges toward the girls as they run toward Joel's house. In the next frame Guido is standing back where he was before he started running. Guido charges, then stops. He never runs. He is standing where he started because he knew that chasing them would be futile, hence his reaction (throwing down the clothing) to his frustration over their behavior.

When Lana is running across the lawn, she's barefoot, but in the very next scene, when you see her running from behind, she's wearing heels. Frame by frame analysis reveals that she is wearing shoes, evident by the little red straps of her shoes.



Revealing mistakes

Miles calls Jackie to arrange a date with Joel but when Joel objects and asks for the number, Miles eats the paper upon which it is written. As Jackie arrives it is obvious Joel had been unable to contact him/her to prevent this from happening (despite having time during the rest of the day to find the number by other means). Later when Joel and Miles are in the hotel looking for Lana, Joel tells Miles that he called Jackie and was told that Lana might be there. However, Joel obviously has no way of contacting Jackie or finding his/her number (at the very least if he did he would have used it before)

When Guido is following Joel, Lana and Miles down the freeway when he starts honking his horn if you look through Lana's window a car can be seen travelling in the opposite direction clearly as a result of some kind of projection error.

The leaf-raking scene near the end of the movie is supposed to be windy, but the only leaves blowing are the ones at Joel's feet. The giant trees surrounding the backyard aren't even rustling.

'Jackie's' ad in the paper reads "For a good time in the privacy of your own home, call Jackie, 555-4875." (Miles also says the ad is succinct, implying that this is all that is written). However, when Jackie arrives at Joel's home it is obvious 'she' is a man dressed in women's clothing, and from Joel's reaction this is not what he expected (or wanted). Jackie then says to Joel, while waiting for a cab, that "When you put your good money down you got to get what you went after in the first place." But all the ad implies is that a girl called Jackie will arrive when you call and nothing else. Which means that almost everyone who calls will not 'get what they went after' and hence Jackie should constantly be arriving at people's homes and leaving right away, as is the case with Joel.

After the Porsche is pulled out of the lake it is shown sitting on a tow truck in the repair shop. Before the car door is opened, underneath the truck and car are several medium-sized fish. However, there is no reason for these fish to be there. After all, it is only after the car door is opened that a large quantity of water plus fish come out.



Audio/visual unsynchronized

When leaving the Drake with Lana, and Guido approaches the Porsche 928, the back-up light flash momentarily before departure (this would indicate an automatic transmission passing through reverse). All sound effects indicate a manual.

In the brothel scene, when the hooker places her hand on the boy's knee and scares him away, we see a drummer and a pianist playing in the upper left-hand corner of the screen, but we hear a recorded version of "D.M.S.R" by Prince. They are also visible just before Joel complains to Lana that some of the girls are wearing his mother's clothing, and once again we hear recorded music.

The 6000 series "L" uses dynamic brakes and not air brakes, during many of the "L" scenes you can hear the sound of air brakes releasing.

When Joel is driving with Barry discussing the meaning of "boffing," the rear hatch of the Porsche 928 is bumping up and down because it isn't locked. It rattles loudly and the wiper arm jiggles noticeably, because the rear hatch lock sits in a polyurethane sound deader.



Crew or equipment visible

When Lana enters Joel's room while he is studying, a crew-member grabs the doorknob.



Errors in geography

Joel and Miles see Lana in the hotel lobby of the Ritz Carlton Chicago but exit the Drake Hotel.



Character error

In the Princeton interview, Joel states that he wishes to major in business. Princeton has never offered a business major.

when Joel's Dad tells him to not mess with the stereo, he readjusts the equalizer to his liking (which is off), turns off the tape deck (which is on), then turns ON the equalizer.

When 'Jackie' leaves without providing any services she asks Joel for 75 dollars for her time and cab fare. Joel then spends the whole night with Lana but acts surprised when she asks for more than the 50 dollars he has in the house. He should have known from his experience with Jackie that he would have needed a lot more than this and would have gone to the bank earlier in the day or obtained the money some other way.