Factual error: The film is supposed to be in Alabama, but it was actually shot in Georgia. You can see this when Vinny and Mona are first pulling into the town and they are turning left, in the shot you can see the Georgia State Highway road signs off in the distance. (00:13:20)
Factual error: In District Attorney Trotter's opening statement he asks the jury to convict William Gambini of murder in the first degree and Stan Rothenstein of accessory to murder in the first degree. There is no such crime in the Alabama criminal statutes. It has to be either Capital Murder or just Murder. Alabama does not have different "degrees" of murder. Also the arraignment and trial are both conducted by the same judge. In the Alabama court system a District judge would have conducted the arraignment, while a different Circuit judge would have conducted the jury trial. It's ironic since the director brags about his attention to detail in the DVD director's commentary. He obviously didn't check it too closely.
Factual error: As an out-of-state attorney, Vinny would have had to file documents for admission to the state bar association "pro hac vice" ("for this case"), and the boys would have been assigned a local attorney to ensure compliance with the rules of procedure, which Vinny kept violating.
Factual error: When Lisa is testifying about the 1963 Pontiac Tempest and the 1964 Buick Skylark being the same height, width, and wheelbase. While the Tempest and Skylark shared the same components, the 1963 and 1964 models were quite different from each other. The 1964 Skylark and Tempest moved to a 115 inch wheelbase and a larger body and frame. The 1963 Skylark and Tempest were smaller with a 112 inch wheelbase. It is hard to believe that someone would confuse a 1963 Pontiac Tempest convertible with a 1964 Buick Skylark as they were completely different cars with a different height, width, and wheelbase.