Continuity: When Charles Bronson steps out on the balcony of the nazi villa a second time (after having to hide), he drops his rope (to get on the roof), and when we see him from another angle, he drops it again.
Great sites
Mistakes
When the four remaining guys finally cross over the bridge in the half-track, John Cassavetes gets shot dead by a Nazi soldier. The next shot shows the vehicle just crossing over the bridge again. See more...
The Dirty Dozen mistakes
Factual error: When Resiman interviews him in prison, Franko is chewing gum. (In several shots you see it is chewing gum and not tobacco). First, during heavy rationing in the UK in World War 2 chewing gum was a rare and expensive treat. A military prisoner would not be able to obtain it for love or money. Secondly, US military prisoners were never, ever allowed chewing gum - it can be (and has been) used to jam locks.
Continuity: When the four remaining guys finally cross over the bridge in the half-track, John Cassavetes gets shot dead by a Nazi soldier. The next shot shows the vehicle just crossing over the bridge again.