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.
Continuity mistake: After Louis asks if anybody wants to play Parcheesi at his party, there is a lady sporting a red vest behind him, standing in front of a wall with framed photos. Two shots later, she's standing in front of the kitchen next to a bespectacled man. The very next shot, she's teleported back to where she was initially, in front of the wall. (00:53:25)
Continuity mistake: When the Ghostbusters are heading for the building, there's a wide view of New York bathed in a sunset light with a red and blue sky. In further close-up shots, there is a clear sunny light everywhere. (01:15:20)
Continuity mistake: At the end of the movie when everyone is waving to the Ghostbusters and Ray is backing up the car, on the light bar on Ecto 1, the outer lens is a solid blue light bar. When the car goes to drive away, it's a clear light bar with blue lens covers over each individual rotator.