The case of a 8 month-old infant presenting with biliary peritonitis, mild icterus and slowly progressive ascites is reported. Diagnosis was made through paracentesis showing higher bilirubin levels in the ascitic fluid (18 mg/100 ml) than in serum, and abdominal ultrasonography which showed pictures suggestive of choledochal cyst. A perforated choledochal cyst was surgically removed. The biliary duct was reconstructed by means of a hepatic Roux-en-Y jejunostomy. Postoperative course was satisfactory.