Factual error: Early in the film, when Henry Hill is selling Pall Mall cigarettes out of a car trunk and is arrested, there are UPC price codes visible on the cartons of cigarettes. UPC codes were not used on products in the 1950's when the scene is taking place. They were introduced in the mid 1970s.
Factual error: In the scene where Henry pistol-whips Karen's neighbor, Henry is driving a 1966 Chrysler, when it 1964 at the latest. We know this because at the end of the movie it says that Henry and Karen were divorced in 1989 after 25 years of marriage. That means they were married in 1964.