Abdominal actinomycosis in childhood period is very rare and a relation to trauma is not well established. Herein we report a case that appeared subsequent to abdominal trauma. A 17 years old boy presented with left lower quadrant abdominal mass and signs of acute abdomen. The symptoms of abdominal discomfort began after a fall from height 3 months before admission. There were signs of acute abdomen at physical examination. Ultrasound of abdomen demonstrated a mass; CT scan findings pointed to a suspicious "internal hernia". An emergency laparotomy was performed. During surgery, a mass located over sigmoid colon and infiltrating the lateral abdominal wall was found. It was removed en bloc with the adjacent omentum. Except for the thickened sigmoid colon, no other pathologies were present at laparotomy. The pathology specimen revealed the actinomyces infection. The patient was treated with oral penicillin after discharge and the follow-up was uneventful. We advocate, keeping the actinomyces infection in mind in cases presenting with abdominal mass of unknown origin in childhood period.