A rare case of primary hydatid cyst of the mesentery is described. Though cystic echinococcosis infestation can occur in any part of the body primary peritoneal involvement is rare. The mechanism of primitive peritoneal infection by the parasite is still unclear. The hypotheses which can explain this rare primary localization, the sensitivity and the specificity of the serological and instrumental tests and the therapeutic management of this atypical lesion are discussed.