Severe neonatal cholestasis is a clinical problem requiring a differential diagnosis of intra- (hepatitis) and extrahepatic (biliary atresia) causes, prognosis and therapy being different in the two cases. Eighteen patients of pediatric age underwent US and hepatobiliary scintigraphy. US findings were aspecific in both hepatitis and biliary atresia. In the 11 patients with hepatitis, hepatobiliary scintigraphy after phenobarbital revealed labeled bile in the bowel. Only in 1 patient with cytomegalovirus hepatitis was a scintigraphic pattern similar to that of biliary atresia. On the contrary, no intestinal radioactivity within 24 hours was seen in 6 patients with biliary atresia. A portoenterostomy (Kasai's operation) was performed on 4/6 cases with biliary atresia. These patients were followed with hepatobiliary scintigraphy in order to evaluate anastomotic functionality. In a case of biliary cirrhosis secondary to occlusion, orthotopic liver transplantation was performed whose success was scintigraphically monitored. Our results point to hepatobiliary scintigraphy after phenobarbital as the best noninvasive procedure for both diagnosis and postoperative follow-up of biliary atresia. Labeled bile excretion within 24 hours was rarely found in both atresia and neonatal hepatitis.