Epididymal tumors are uncommon and usually benign, with only 25% of them being malignant. Undifferentiated epididymal carcinoma in particular is extremely rare. We report on a 54-year-old male patient presented with right testicular pain and scrotal mass for the last 6 months. Laboratory investigations were unremarkable but epididymal biopsy result was epididymal undifferentiated carcinoma. Inguinal radical orchidectomy was performed and pathological examination of the surgical specimen confirmed the presence of undifferentiated carcinoma. Then, adjuvant chemoradiotherapy (four cycles of cisplatin-etoposidc chemotherapy and radiotherapy) was administered. After four months, lung metastases were detected and three doses ifosfamide-Adriamycin chemotherapy were given, but the patient died clue to the disease progression. Reports of epididymal undifferentiated carcinoma are extremely rare and the present report emphasizes the need of including epididymal undifferentiated carcinoma in the differential diagnosis of an epididymal mass.