In a study from 40 hospitals in Western Japan between 1975 and 1978, intrahepatic gallstones were identified at the first biliary tract operation in 106 patients (a 3.03% prevalence). These were predominantly bilirubin stones. The occurrence rate for patients with intrahepatic stones was the same as for patients with bilirubin stones solely in the common bile duct suggesting the pathogenetic similarity of these two conditions. The prevalence of intrahepatic stones was 1.5% at urban and 4.97% at rural hospitals (P less than 0.005). Rural patients were significantly older than urban patients (P less than 0.005), but both groups showed an increasing prevalence with age. However, patients with intrahepatic stones were younger than those with bilirubin stones solely in the common bile duct, reflecting the increase likelihood that stones obstructing the biliary tree in this location would cause hepatic damage, pain, and, fever or the possibility that congenital anomalies of the bile ducts migt lead to stone formation at an earlier age. Among the 106 patients, only 12% had stones in the intrahepatic ducts alone. The majority of patients with both bilirubin and cholesterol intrahepatic stones had stones throughout the biliary tree simultaneously. The decreasing prevalence of bilirubin stones in Japan may be related to multiple factors including eradication of parasites and westernization of the diet.