Continuity mistake: At the Lincoln Center (that place Dana's orchestra plays at) the nerd with her has his case and they're leaving when Peter is there. Nerd-boy goes off to the side and waits. When they start off again, his case pops back and forth unhumanly between being carried under his arm and in his hand between long and close shots about 3 times. (00:44:34)
Other mistake: After the guys decide to rent the building, the shot of New York from the park is the very same one, though with different sky colour, to that of the moment when they are about to battle Gozer. Though it's a very wide and common shot of the park, the very same people are laying on the grass in the very same position in both shots (big screen recommended to spot it).
Visible crew/equipment: When Dana arrives at the Ghostbusters' office, a crew member can be seen moving behind the filing cabinets behind where Janine is sitting. It could be Venkman, but even after Venkman walks over to Dana, there's still a rogue hand there, showing us it wasn't Venkman and was a crew member. (00:22:10)
Factual error: When Dana first arrives at her apartment building, you can see a view of her getting ready to cross the street the front door from above, and the demon dog statue's head is in the shot, looking down. If that building is as high as they make it out to be, the distance between the dog, which is on the roof, and the street would be a lot more than it is in the shot. You probably wouldn't even be able to see Dana from that height.
Continuity mistake: When Dr. Venkman is looking in Dana's refrigerator the items on the top shelf shift position, disappear and/or are replaced with other items. The large glass dish that was on the left of the Coke can is replaced by a small plate of food. The Coke can turns. There is also now a large bottle behind the Coke can. Clearly these 2 connected shots were filmed on different days and the items were stocked without regard for the previous shots items and positions.
Continuity mistake: When the 'disgusting blob' goes through the wall above the vase of ferns after being attacked by Ray, you can see two small amounts of slime appear on the wall. In the next scene, when the food trolley crashes into the table, there is more slime on the wall than there was in the previous shot.
Continuity mistake: Venkman meets Dana by a fountain. When he says goodbye to her, first a man with a hat passes behind him and disappears in the next angle; then, in a close-up, Venkman is surrounded by dozens of people who vanish half a second later in the wide angle, where the place appears empty.
Continuity mistake: When Egon tries to prevent Walter Peck from shutting down the protection grid, he has Janine and Vinz (Louis) behind him. You can see that Vinz is raising his right arm, but in the next shot his right arm is now lowered down.
Continuity mistake: When Dr. Venkman investigates Dana's refrigerator, there is a Corning dish and a can of Coke side-by-side on the top shelf. The camera cuts twice, and there is suddenly another item (looks like lunch meat) that appears in front of the Corning dish and the Coke can.
Continuity mistake: In the scene where the earthquake begins, the Ghostbusters fall into a hole. They're in two rows - in the first row are Venkman and Ray and in the second row are Egon and Winston. In the following shot, it is now Ray and Winston on the first row and Venkman and Egon on the back row. (01:20:30)