Continuity mistake: At about the middle of the film, when the Ghostbusters are rising to fame and are appearing on the front of newspapers and magazines, the photograph on the front of the New York Post is taken from the end of the film, just before the four of them cross the streams from their proton packs.
Revealing mistake: Towards the end, when the ground is shaking and breaking up, a police car falls halfway into a hole in the road. When the smoke clears a little you can clearly see two white poles, one on either side of the back left wheel, holding the car in place.
Revealing mistake: In the ballroom scene, when Slimer is flying around the chandelier, he disappears for a few frames when he reaches the far side. [This animation is mentioned in the DVD commentary. The film makers were generally unhappy with the entire animation and the fact that the representation of the apparition did not resemble those previous and that the movement was very unconvincing.]
Continuity mistake: The Stay Puft Marshmallow Man has a red bow tie on as he walks down the streets of New York, which disappears in one shot as the Ghostbusters fire at him.
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.
Revealing mistake: In the earthquake scene where the road is cracked, you can see the cloth on the side of one of the cracks flapping in the wind.
Continuity mistake: When the eggs pop out of her bag and start cooking on the counter, they're in different positions depending on whether it's a close up or wide shot.
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.
Revealing mistake: Near the end of the film when the Ghostbusters take cover in a small corner and come up with the "cross the streams" plan, look closely at Peter's proton pack, you can see that it is a foam "stunt" pack as there is a small sticking out part that keeps squashing against the wall behind him.