Fetus-in-fetu: report of a case.

A case of fetus-in- fetu is reported. It occurred in an 8-week-old Korean boy who had been born by cesarean section due to abdominal distension. The fetus-in- fetu was connected to the superior mesenteric artery and consisted of two masses, apparently representing two portions of an acardiac monster. There was an amniotic membrane covering both masses, and the umbilical cord clearly was identifiable. One mass included the brain, eye, trachea, salivary glands, thyroid, pancreas, spleen, etc., while the other mass contained extremity bones, vertebrae, testis, adrenals, and intestinal loops. This is probably a case of separated fetus-in- fetu that showed unusually well-developed internal organs.