Background: In testicular carcinoma the early diagnosis is very important because with an early therapy there are good chances for long-term survival (50–90%). Metastases of a testicular carcinoma are at first lymphogeneous, hematogeneous only in late stages. Case Report: This is a case report about a 28-year-old man, whose testicular carcinoma (left testis) had already been operated on (unripe teratoma with parts of an embryonic carcinoma, an endodermal sinus tumor and a chorion carcinoma). Because of the elevated tumor marker AFP an FDG PET (F18-fluorodeoxyglucose positron emmission tomography) investigation was made. CT (covering thorax, abdomen and pelvis) and ultrasound of the testis showed no pathological results. In the FDG PET a significant pathological FDG uptake in the right testis was found. Histology showed an unripe teratoma with parts of an embryonic carcinoma, an endodermal sinus tumor, and a chorion carcinoma. It was a second carcinoma of the contralateral testis. Conclusion: F18-FDG PET was a sensitive and reliable modality for diagnosis in this patient.