Omental cyst is benign unilocular or multilocular endothelium-lined cyst that contains either chyle or serous fluid. They are uncommon yet interesting intraabdominal masses that may be difficult to diagnose clinically and often are missed on abdominal palpation. The etiology of this lesion has been subject to much discussion in the literature over the years with the principal debate centering around the question of whether or not this lesion is congenital. It is now recongnized that there is no single etiologic mechanism involved in the development of this lesion. Recently we have experienced an autopsy case of omental cyst occurring in a male fetus. Pregnancy was artificially interrupted at 28 weeks gestation due to suspicious mesenteric cyst or fetal ascites on ultrasonography. Postmortem examination showed hydrops fetalis, hypoplasia of the lungs, ad multifocal calcifications of myocardium. There was an omental cyst in the greater omentum which was 7x3 cm in size, unilocular and containing clear, straw-colored fluid and proteinacious core without evidence of bleeding or calcifications. Microscopic examination of this cyst showed cuboidal or flattened mesothelial lining cells and underlying loose fibrovascular connective tissue with discrete lymphocytic collections. Rarity and interest on the pathogenesis made us redport this case.