The relationship between duodenal diverticula and age, sex, and biliary calculi was studied prospectively in 624 patients examines with endoscopic retrograde cholangiopancreatography (ERCP). The study showed that the incidence of biliary calculi was significantly higher in patients with diverticula (86%) than in patients without diverticula (38%). The difference was significant in all age groups above 40 years (p less than 0.01). The rate of diverticula found near the papilla of Vater was significantly higher in patients with biliary calculi than in patients without (p less than 0.01). A positive correlation was found between age and diverticula but not between sex and diverticula. An insufficient papillary sphincter together with an ascending bacterial infection is discussed as a possible explanation for the higher incidence of biliary calculi in patients with duodenal diverticula.