We report a case of a young man with a rare disease, a choriocarcinoma of the gastrointestinal tract presenting as a common entity, a bleeding duodenal ulcer. Pathological findings and strongly positive immunostains of tissue specimens for beta human chorionic gonadotrophin confirmed the entire tumor to be a choriocarcinoma ruling out the possibility of an adenocarcinoma with focal components of choriocarcinoma or a beta human chorionic gonadotrophin producing adenocarcinoma. The pattern of tumor invasion in this case is more suggestive of metastatic than primary involvement of the gastrointestinal tract. The diagnosis of primary gastrointestinal choriocarcinoma is difficult because of the need to meticulously rule out the occurrence of a primary in other organs, which at times regresses spontaneously, a diagnosis made more difficult in this case in which no autopsy was performed.