BACKGROUND In contrast to adults, little is known about the epidemiology and the best therapeutic regimen for cholelithiasis and sludge in children. METHODS Eighty-two children with cholelithiasis detected by ultrasonography were studied from 0 to 18 years of age with regard to cause, symptomatology, and treatment outcome. Seventy-five children with sludge within the same age group were studied as well. RESULTS Idiopathic gallstones were found in 19 (23%) patients, and 32 (39%) had gallstones in association with a hemolytic disease. Predominant factors associated with the development of gallstones and clinical presentation differed with age. In patients with sludge, total parenteral nutrition and systemic infection or administration of antibiotics were most frequently found to be possible predisposing factors. Sludge can develop and disappear within a few days. Complications of cholelithiasis were observed in 13 patients. Cholecystectomy was performed in 41 patients and therapeutic endoscopic retrograde cholangiopancreatography (ERCP) with stone extraction in 9 patients; 32 children were not treated. After a follow-up (mean, 4.6 years) in 50 patients, 46% of the children who had cholecystectomy or therapeutic ERCP experienced clinical recurrence of abdominal symptoms. In the patients who did not receive surgical or endoscopic therapy during the follow-up, no complications occurred, and only one patient experienced abdominal symptoms during follow-up. CONCLUSIONS The difference in associated conditions may indicate that the pathogenesis of cholelithiasis and sludge differ as well. Furthermore, sludge should be viewed as a dynamic condition not predisposing for the development of gallstones, per se. Cholecystectomy should not be performed routinely but only after careful selection in patients at risk for complications.