Revealing mistake: During the final fight with the Goblin, Spider-Man is up against the wall and the Goblin goes to stab him with his "quad bladed knife". Spider-Man grabs 2 of the blades and while pushing back you can see all 4 ends of the blades vibrating up and down as if they were made out of rubber.
Continuity mistake: When Mary Jane is being mugged by four men, Spider-Man throws two of the men into two windows behind Mary Jane. The shot switches to Spider-Man beating up the other two guys. When it cuts back to Mary Jane the two windows are intact.
Continuity mistake: When Peter shoots his web at his bedroom lamp and pulls it across the room, it smashes against the wall and breaks. But when Aunt May is talking to Peter from the door seconds later, the lamp is back on the dresser in one piece.
Continuity mistake: When Norman is getting ready to test himself, he lies down on the bed, fastens himself in and the doctor goes to the computer. However, when it shows him being brought in to the chamber he has several electrodes connected to his chest and head.
Revealing mistake: When Peter Parker first discovers he can climb up walls (while in citizen clothing), he tests it out by climbing up a building in an alley. During this scene, you can clearly see his clothes hanging out forwards, indicating that the scene was filmed with him crawling along a floor horizontally.
Continuity mistake: The scene at Columbia University was filmed on an unseasonably warm spring day, however, the costume department had provided the high school extras with cold-weather clothing. The real Columbia University students can be seen in the background wearing shorts and t-shirts by contrast.
Continuity mistake: In the final battle, the blood on Spider-Man's chin and under his nose keeps disappearing and reappearing.
Other mistake: When Jameson is flipping the pictures of Peter's first batch of photographs, you can see (in slow motion or if you have really good vision) that the 3rd picture he looks at changes into an entirely new photograph, when he puts it down. The one he's looking at is Spider-Man on the side of a building, but when it's on the desk it's Spider-Man kicking a thug in the face. The one he then looks at changes too - it was about to have a bit of sky on the left, but then turns into a photo of a street from above, with no sky visible.
Continuity mistake: When Spider-Man saves the baby from the burning building, it's amazing that the baby and the blanket are so clean - no soot, smoke damage, charring, etc. The firefighters have obvious soot around their noses from trying to breathe in that area. Did Spidey manage to give the baby a bath before presenting it to momma?
Continuity mistake: When Peter first learns he can climb walls after running out of school, his shoes are different when he is on the wall compared to when he is on the roof.
Continuity mistake: When Spider-Man is chasing the crook with the gun, the crook shoots 7 times through the roof of the car. Shortly afterwards you can see 9 bullet holes in an overhead shot. As the scene moves along there is another overhead shot (just after Spider-Man jumps the bridge) - no bullet holes. Seconds later the bullet holes return.
Other mistake: When the tram with all the kids is falling, the kids are yelling. The adult behind them isn't yelling & looks bored.
Factual error: When Harry is talking to Mary Jane on the phone, she hangs up on him and his cell phone produces a dial tone. Cell phones do not have a dial tone.
Continuity mistake: When Peter is drawing up ideas for his costume the hand is that of comic artist Phil Jimenez, current artist of Wonder. Phil Jimenez is right handed and Tobey is left handed. In one of the cuts the pen is in Tobey's left hand but it shows him drawing with his right.
Continuity mistake: During the kiss scene the camera changes view back and forth. From one angle it's raining, in other it is not, then at the end it's pouring as if in a storm. They had to do that scene at least 3 times.
Continuity mistake: During the World Unity Festival, the Green Goblin seeks revenge upon his ex-coworkers. The Goblin throws a pumpkin bomb at them that makes them all disintegrate and disappear. One of his coworkers had a wheelchair with him, which survives the Goblin's bomb and remains on the balcony. (You can see the wheelchair while they are being bombed and after they disintegrate, all in the same shot.) For the rest of the scene, the wheelchair has disappeared from the balcony.
Continuity mistake: In the cafeteria scene, Mary Jane slips on some spilled orange juice that causes Peter to catch her. A short while later when Peter gets up to leave the cafeteria, running away from her enraged boyfriend, the spilled orange juice is not there.
Continuity mistake: When Peter is taking out the trash, and begins talking to Mary Jane, as she walks toward him you can see her underwear sticking out above her pants. As the shots change, this underwear seems to appear and disappear.
Continuity mistake: In the final cemetery sequence, Peter and Mary Jane square off for a little heart to heart, with her touching his face tenderly with her black leather gloves. The camera intercuts between front views of both: in hers, her fingers are touching his ear lobe, in his, they are a inch below his ear lobe. In one quick cut of hers, the hand has disappeared completely, then in mid-sentence as they cut back to Peter, it's there again.
Continuity mistake: During the World Unity Festival when the Goblin attacks, there is a shot of Peter tearing off his shirt exposing a costume that is low cut at the neck. However, in the scene when Spider-Man and Mary Jane kiss in the rain, the costume comes halfway up his neck.