Cisplatin has played a major role in the treatment of germ cell tumors. However, it causes renal damage, severe nausea and vomiting. It is also neurotoxic and ototoxic. Carboplatin is an analog of cisplatin which, does not cause renal damage at therapeutic doses. It is not neurotoxic or ototoxic and it produces less gastrointestinal toxicity than cisplatin. We used carboplatin alone as an initial chemotherapy in a 36-year-old man with stage IIB seminoma. Following left radical orchiectomy the patient received 4 courses of carboplatin chemotherapy. After the first course of chemotherapy, tumor markers (LDH, beta-HCG) returned to the normal range. After 4 courses, the size of the retroperitoneal metastases was significantly reduced. The toxicity of 4 courses of carboplatin chemotherapy was generally milder than that of cisplatin-based combination chemotherapies such as PVB or VAB-6. There were no episodes of septicemia, thrombocytopenic bleeding or renal deterioration. The patient did not suffer from alopecia, neuropathy, symptomatic hearing loss, severe nausea or vomiting. Nine months after the completion of carboplatin chemotherapy, the patient remains well and free from disease progression. This case strongly suggests that single agent carboplatin therapy could be an effective and less-toxic treatment for advanced seminoma.