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.
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)
Continuity mistake: When Ray and Winston are driving back to the Ghostbusters' office, Winston (who is driving) is wearing coveralls; when they arrive and get out of the car, he is wearing just a shirt and trousers. (01:04:00 - 01:08:20)
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. (00:16:50)
Continuity mistake: Louis/Vinz Clortho is dropped at Ghostbusters office at night at the same time Venkman is drugging Dana/Zuul at her apartment. When Venkman calls from her apartment it is night, Janine is in the same grey striped blouse, black skirt and tights outfit during that call she was wearing when Louis was dropped off by the police, at this time Venkman says he is on his way back to the office. Venkman does not arrive until the next morning, during the EPA raid, he is still wearing his same brown date night jacket and blue shirt but it's daylight now and Janine has changed into a new outfit, red blouse, grey vest, grey skirt and red tights and does not look like she slept at the office, Egon has also changed at least his tie and put on a suit jacket.
Continuity mistake: When Dana comes to the station for the first time, Ray is working on Ecto1 and it's primer gray, no light bars or equipment. In one of the following scenes they are eating dinner and cheering to their first customer. Then the alarm sounds for their first call to the Sedgwick hotel and they get in the Ecto1 that is all tuned up, painted with lights and equipment mounted. The events all appear to happen in the same day. It wouldn't be possible to do all that work to Ecto1 in the perceived span of time. (00:21:50)
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. (00:33:15)
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. (00:44:45)