This is a case report concerning a 2 years-old white boy who suffered sepsis fever with isolation in blood culture of an anaerobic bacteria (Ristella or Bacterioïdes fragilis). Despite continued specific therapy with clindamycine, a mass rapidly developed in the upper left portion of the abdomen which was investigated by plain film, barium enema, upper G.I. series and ultrasound study. The diagnosis of splenic abscess was only made at laparotomy. Splenectomy was a difficult procedure and needed an extension to the chest because of diaphragmatic adhesions. Culture of pus from the excised spleen grew bacteroides fragilis also, and metronidazole was added for therapy. Recover was uneventful with a 3 years follow-up. The authors emphasized the difficulty of clinical diagnosis of splenic abscess, the difficulty of bacteriological study of anaerobic bacteria and the scarceness of such cases, especially in pediatric literature. They ask the question about the legitimacy of splenectomy.