We report a case of a histologic grade II endometrial adenocarcinoma without trophoblastic differentiation in a 24-year-old woman with an elevated serum concentration of human chorionic gonadotropin (hCG) and with no evidence of pregnancy. Serum and urine specimens were used to study the hCG immunoreactivity. Qualitative tests performed on serum and urine using 5 different assays produced conflicting results. The hCG concentration in serum and urine was quantified using assays designed to detect different molecular forms of the molecule; analysis revealed that serum hCG immunoreactivity was due entirely to the presence of the free beta subunit. Immunohistochemical analysis performed on tissue samples showed strong cytoplasmic staining for hCG. While hCG is a well-recognized tumor marker in gynecologic malignant neoplasms, immunoreactivity most often is due to the presence of both intact molecule and the free beta subunit. To our knowledge, this is the first report of an endometrial adenocarcinoma producing only the free beta subunit of hCG.