A 31-year-old woman with a history of infection with human papilloma virus was found to have an elevated human chorionic gonadotropin level (beta-HCG) of more than 9000 IU/L in January 2006. The patient reported an irregular menstrual cycle. Extensive clinical work-up including gynecologic examinations with laparoscopy, hysteroscopy, and curettage were performed but no pathologic explanation of this elevated beta-HCG could be found. In the initial computed tomography (CT) of the abdomen and the thorax, a tumor could not be detected. Based on a clinical decision, chemotherapy with methotrexate in a dose of 1 mg/kg body weight was started. Four months after beginning of the chemotherapy the beta-HCG level dropped to 3048 IU/L. At this time a first F-18 FDG PET was performed and the findings were negative. After completion of 7 cycles of chemotherapy the beta-HCG level rose again. In a second F-18 FDG PET in August 2006 focal, intense and pathologic F-18 FDG accumulation with a SUV max. of 5.4 was seen in the mediastinum in the region of the thymus. At this time the beta-HCG level was 7000 IU/L. In a subsequent CT of the chest a retrosternal mass of 4 x 1.7 cm was detected with contrast enhancement. Resection of the tumor and thymus gland demonstrated a choriocarcinoma in part adjacent to the thymus and in part in the thymus. Postoperative beta-HCG levels dropped to 105 IU/L.