Hydatid disease is an endemic disease in certain areas of the world. It is located mostly in the liver. Spontaneous rupture of the hydatid cyst into the peritoneum is a rare condition, which is accompanied by serious morbidity and mortality generally. We present herein a case with a spontaneous rupture of a hepatic hidatid disease into the peritoneum without any serious symptoms. A 15-year-old boy was admitted to the emergency room with a mild abdominal pain lasting for a day. Physical examination revealed only mild abdominal tenderness. There was no history of trauma or complaints related to hydatid diseases. Ultrasonography showed a large amount of free fluid and a cystic lesion with irregular borders in the liver. He was operated on. Postoperative albendazol therapy was given for 2 mo. No recurrence or secondary hydatidosis was seen on CT investigation in the 3rd, 6th and 12th mo following surgery.