The authors report the case of a hepatic artery aneurysm which ruptured into the peritoneal cavity in the course of acute, gangrenous cholecystitis, which was treated successfully. The clinical aspects of the case, its evolution and the histological study, which appeared to indicate that adjacent inflammation was the cause of the rupture, are discussed. Treatment of hepatic artery aneurysms is conditioned to a great degree by the gravity of the onset, and in most cases ligature is the only feasible procedure. Other forms of treatment may be possible when the aneurysm is intrahepatically located or it is diagnosed before rupture.