Continuity mistake: When the hotel manager refuses to pay the bill after the Ghostbusters capture the green ghost (Slimer), you can see he is putting his handkerchief into his top pocket with his left hand, but in the very next shot he can be seen putting the handkerchief in the pocket with both hands.
Continuity mistake: The large blue book that Peter drops on the table to startle Egon disappears off the table in the next shot. (00:07:10)
Revealing mistake: When the Stay-Puft Marshmallow Man is walking through the city, in several shots you can see outlines of people and buildings through the marshmallow man, who was added in optically. (01:32:05)
Continuity mistake: At one point in the movie we see the end of the hallway in Dana's apartment and the end is of a window and the wall around it is red like the end near Dana's door. However, (either when the Ghostbusters arrive at the end or when Louis is being attacked by the terror-hound) the whole hallway (even the other end) is all white. (00:17:15 - 00:53:30)
Continuity mistake: When the mayor orders Walter Peck out of his office, you can see that he is pointing his finger at Peck, but when the camera angle changes his hand is nowhere to be seen.
Revealing mistake: A shot from above Dana Barret's apartment, from just above a statue looking down on the road below: The statue in the foreground is partially transparent. We can see the double yellow line on the street go straight through one of the statue's upper fangs, and one of the white lane dividers going through the statue's lower jaw. Viewed on Bluray disc. (00:16:50)
Continuity mistake: When the guys blast the glass lamp in the hotel, it falls on a table and messes up the table and chairs around. In the following angle the chairs are in a different position and the area, which was dark half a second ago is now perfectly lit, without anyone having moved and, most important of all, after the big lamp has been shred to pieces.
Revealing mistake: As Dana's apartment crumbles apart to present the temple of Gozer, there is a tight shot of a gargoyle falling off an exterior corner. Carefully lined up with features on the gargoyle's face - but still readily visible - are the black strings that pull the gargoyle face off its mount.