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)
Trivia: The Ghostbusters theme, "composed" by Ray Parker Jr., was directly ripped off from the song "I Want A New Drug" by Huey Lewis and the News. In fact, Huey Lewis sued Ray Parker for intellectual property theft (settled out of court). Premiere Magazine later featured an article in which the film makers admitted to using the song "I Want a New Drug" as temporary background music in many scenes. They said that they made an offer to Huey Lewis to write the main theme for the movie, but Huey Lewis declined. The filmmakers then provided Ray Parker Jr. with finished film footage (including the Huey Lewis song in the background) to aid Ray Parker in writing an original theme song, which apparently he couldn't do.
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: 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.