Incidence of juxta papillary duodenal diverticula (JPDD) was studied in 182 patients with benign biliary diseases. Incidences of JPDD were 11.1% in cholecystolithiasis, 23.4% in cholecystocholedocholithiasis and 54.5% in choledocholithiasis. Concerning to the patients with common duct stones, average of age was significantly higher in the group with diverticulum than in the group without diverticulum (65.9 +/- 7.6 vs 55.9 +/- 13.7, p less than 0.01). Diameter of the common duct was also significantly larger in the group with diverticulum. To exclude the effect of aging, the same comparison was performed in patients older than 60 years. Here again, the group with diverticulum showed significantly greater dilatation of the common duct. Incidences of JPDD in the primary and secondary common duct stones were 73.1% and 19.7%, respectively. The difference was highly significant. JPDD seemed to play an important role in the pathogenesis of cholestasis in the aged patients which may result in formation of primary common duct stones.