Ulcers of the lower legs caused by arteriovenous fistulae show, on one hand, that diagnoses are often made carelessly and, on the other, that the treatment initiated is often inadequate. In both cases reported, there were several small arteriovenous fistulae in the lower legs, although no symptoms were observed for a long time. The ulcers, which then recurred chronically, resulted from very minor injuries. Their characteristics remained unnoticed for many years. Surgical intervention to remove these fistulae is not always simple because they cannot all be removed at once. Lower leg ulcers caused by arteriovenous shunts are an example of how difficult it can be to prove the cause of such lower leg ulcers.