The patient was a 54-year-old man. At age 6 years, he had undergone orchiopexy for left undescended testis. Six months prior to the current presentation, he visited our hospital with a chief complaint of painless enlargement of the left testis. Left high orchiectomy was performed under a diagnosis of left testicular tumor. Histopathological examination determined the tumor to be a seminoma (pT2). Postoperatively, the patient was placed on surveillance without preventive radiation treatment. He visited our hospital six months after surgery due to a painless mass in the right inguinal region. All tumor markers (AFP, HCG-β, and LDH) were within normal ranges. However, based on ultrasound and CT scan findings, lymph node metastasis was suspected and a right inguinal lymph node excision was thus performed. Histopathological examination led to the diagnosis of seminoma.