A 69-year-old man with primary squamous cell carcinoma of the seminal vesicle was successfully treated. The patient presented with complaints of gross hematuria and difficulty in urination. Transrectal ultrasonography revealed a cystic mass behind the bladder, and solid tumorous lesions were visualized in the cyst wall by magnetic resonance imaging. The cystic mass was surgically excised and was verified as the enlarged seminal vesicle with concomitant squamous cell carcinoma. The histopathologic diagnosis was squamous cell carcinoma in the seminal vesicle. Postoperatively, 50 Gy of external beam radiation was targeted to the whole pelvic cavity, and the patient was alive without recurrence 2.5 years after surgery. No other neoplasm was discovered in the body.