A 44-year-old woman presented with an acute abdominal syndrome associated with fever. Laparotomy revealed a mesenteric mass; pathology demonstrated a granuloma containing an adult threadworm (Enterobius vermicularis) and its eggs. Ectopic oxyuriasis is rare, and only three cases of peritoneal granuloma distant from the pelvis or the appendix have been reported previously. Our observation is the first case to which a clinical symptomatology could be ascribed. The pathogenesis and the treatment of this particular localization of oxyuriasis are discussed.