Continuity mistake: Near the end of the movie when the 'false' Buzz Light Year is running along the air conditioning ducts his 'New Utility Belt' disappears then reappears again.
Deliberate mistake: When the characters are crossing the street to get to the toy store, Mr. Potato Head gets his foot stuck on some gum. From the first angle, the gum is at the half way point of the rolling cement drainage pipe. When he barely escapes, the gum is near the lip of the pipe, a foot or so from the end. As the gum sticks to the passing pipe, it appears to be half way between those two points.
Continuity mistake: When Evil Zurg first busts out of his box he looks at Buzz Lightyear running across the parking lot at Al's Toy Barn. Through Zurg's viewfinder, you see Buzz run across a white pair of painted parking lot lines, but when you see an overhead view of Buzz running, he hasn't reached that pair of white lines yet.
Continuity mistake: When Woody asks Jessie to give him 'a little intro' when he is in the cupboard, there is a felt-tip pen by the door of the cupboard. By the time he opens the door, the pen is now 10 yards from where it was before. Woody then runs back into the cupboard to get the polystyrene and when he runs back out again, the pen is now back to its original position.
Continuity mistake: When Woody is in Al's apartment thinking about leaving with the gang, he rubs the brown paint off his boot and looks at the name "Andy" written on it. The direction of the name is written differently, than when the cleaner first painted over it.
Other mistake: When Hamm turns off the TV at the beginning, there's no reflection of him, Rex who is beside him, or the remote.
Deliberate mistake: With upgrades in animation the house Andy's family moved to at the end of the first film has undergone some slight changes. The house is still the same general shape, red in color and with the doors and windows in the same place. But the Toy Story 2 version gained an arch above the front door. Also, in the first movie the house was in front of some large pine trees, there was a straight path from the door to the street, and there was a wooden fence in the front yard. In Toy Story 2 the fence is gone, the path from the front door bends toward the driveway, and the pine trees behind the house are replaced by generic types of trees. The house also is much more detailed (as is most of the animation compared to the first movie), allowing the shading of the brick pattern to come in.