[Situs invertus, a mirror image].
INTRODUCTION: Situs inversus is a rare congenital abnormality often revealed in the childhood. In adults with acute abdomen, it's important to know this organs' inversus for diagnosis and surgery. OBSERVATION: A 36 year-old woman presented with symptoms of appendicitis; she had a complete situs inversus diagnosed in the childhood. Abdominal computed tomography showed signs of diverticulitis but after medical therapy, a colonoscopy revealed a sigmoid tumor. A left colectomy was performed by laparotomy without any particular problems; pathologic examination confirmed a colonic adenocarcinoma T3N0. DISCUSSION: Situs inversus is complete, incomplete or ambiguous. It may be associated with other malformations, especially cardiac abnormalities. When this malformation is unknown in the adulthood, this inversion of organs may be responsible of diagnostic difficulties, especially during the physical examination of an acute abdomen. If the patient underwent surgery, the adaptation to this inversion of organs is relatively easy. In the international literature, the association of this abnormality with colonic tumors seems to be fortuitous.