The incidence of pancreas divisum (PD) was evaluated in a retrospective series of 1,825 successful consecutive ERCPs. One hundred thirty-seven pancreas divisums (7.5%) were found in 80 males and 57 females at a mean age of 49.2 years. The ventral ducts were visualized in 82.5% and the dorsal ducts in 74.1% of attempted cannulations of the minor papilla. Pancreas divisum was significantly more frequent in patients presenting with acute idiopathic pancreatitis (50.0%) or acute biliary pancreatitis (23.7%) than in controls or in the general population. This difference was not found in acute pancreatitis due to other etiologies. Acute pancreatitis associated with PD is generally recurrent, is not severe, but may be complicated by necrotic pseudocysts. The frequency of PD was also significantly increased in patients with gallbladder stones but not with common bile duct stones. In other pathological groups--chronic pancreatitis and pancreatic cancer--the frequency of pancreas divisum was not statistically different from that observed in controls and/or in the general population. We conclude that on a statistical basis, PD is a probable cause of acute pancreatitis, especially in its idiopathic recurrent variety, and that its frequency is increased in patients with gallbladder stones.