During a 17-year period, 40 infants less than 1 year of age were investigated for cholelithiasis; 32 infants were seen within the past 10 years. Seventeen of them had no recognizable predisposing factors. In 6 infants, gallbladder lithiasis was a fortuitous finding on a plain radiograph or sonogram with no signs of common bile duct obstruction; under conservative management, no complications of lithiasis were observed on follow-up of 3 infants and spontaneous resolution occurred in 2 others. In the remaining 34 infants with lithiasis of the common duct or cystic duct or both, the initial symptoms were cholestatic jaundice in 21, acholic stools in 8, sepsis in 4, and abdominal pain in 1. Ultrasonography, performed in 33 of them, showed dilation of the biliary tract in 28, and stones in the gallbladder in 13 and in the bile ducts in 10. Percutaneous transhepatic cholangiography or operative cholangiography in 26 infants showed stones in the bile ducts in 23. In 3 infants, no lithiasis was visible, suggesting the spontaneous elimination of stones. Treatment was initially surgical in 9 infants, but starting in 1981 interventional radiologic procedures were attempted in 15 infants and were successful in 12. Spontaneous resolution of cholelithiasis occurred in 10 other infants with cholestasis. Recurrence of biliary stones was observed in 3 infants only after a follow-up of 7 months to 10 years. These results suggest that common bile duct lithiasis should be considered among the causes of cholestatic jaundice in infancy, and that some of the gallbladder calculi found in older children may have resulted from a lithogenic process that occurred during fetal life or shortly after birth. Percutaneous cholangiography with biliary drainage appears to be an effective means of treatment of infants with common bile duct obstruction; surgery can then be restricted to a limited number of cases, especially those with associated strictures of the bile ducts.