The most common causes of conjugated hyperbilirubinemia after the first or second week of life are neonatal hepatitis and biliary atresia. Since these entities represent varible expressions of same pathologic process and have similar clinical, biochemical, and histologic features, differential diagnosis is extremely difficult. We prospectively studied 28 jaundiced infants by sonography and hepatobiliary scintigraphy. Final diagnoses included 12 biliary atresia and 16 neonatal hepatitis. Visualization of a normal-sized common bile duct ar gallbladder was compatible with the diagnosis of neonatal hepatitis. Non-visualized or atrophic gallbladder on sonography coupled with non-visualization of bowel activity on scintigraphy was highly suggestive of biliary atrenatal jaundice. The combined use of sonography and hepatobiliary scintigraphy provides the most valuable information in suspected biliary atresia for prompt surgical treatment.