Fetus-in-fetu is a rare abdominal tumor of infancy and childhood. In some cases an accurate preoperative diagnosis can be established, while in others diagnosis is not accomplished until laparotomy. Often, the tumor is confused with a teratoma, but with adherence to certain diagnostic criteria, along with a computed tomographic (CT) finding noted in our patient, distinction between the two tumors should be possible before surgical intervention. Our case is presented because the tumor is rare and because it is the first reported case in which CT could suggest the diagnosis preoperatively.