Antenatal spontaneous perforation of the extrahepatic biliary tree. Spontaneous perforation of the biliary system is an unusual neonatal phenomenon that is rarely recognized at birth. To date, it has not been reported antenatally. A 16-year-old pregnant adolescent had an ultrasonogram at 25 weeks of pregnancy that revealed ascites in the fetus. After the infant was delivered at 32 weeks, a hepato-iminodiacetic acid scan showed a spontaneous rupture of the common bile duct. The infant was treated with external drainage of the biliary tree and recovered well. This case demonstrates that spontaneous perforations of the bile ducts can occur much earlier than the usually described 2 to 12 weeks after birth, can be diagnosed antenatally, and should be added to the list of causes of fetal ascites. 