Intraperitoneal metastasis from a testicular germ cell tumor is very rare. We report a case in a 33-year-old man who was referred to Hokkaido University Hospital, Hokkaido, Japan, for further therapy for refractory seminoma. Physical examination revealed abdominal distension as a result of ascites, and cytology of the ascites showed seminoma cells. Although the ascites completely disappeared after treatment with a novel regimen of irinotecan-based chemotherapy, the patient had a recurrence of ascites and died of progressive disease 5 months after the start of the therapy.