From 1995 to 2003, 603 adult patients from Sweden and Norway with metastatic testicular nonseminomatous germ cell tumor (NSGCT) were included prospectively in a population-based protocol with strict guidelines for staging, treatment, and follow-up. Patients with extragonadal primary tumor or previous treatment for contralateral testicular tumor were excluded. The basic strategy was to individualize treatment according to initial tumor marker response. Initial treatment for all patients was two courses of standard bleomycin, etoposide, and cisplatin (BEP), with tumor markers analyzed weekly. Good response was defined as a half-life (t(1/2)) for α-fetoprotein (AFP) of ≤ 7 days and/or for β-human chorionic gonadotropin (β-HCG) of ≤ 3 days. Patients with prolonged marker t(1/2) (ie, poor response) received intensification with addition of ifosfamide (BEP-if/PEI) in step 1. If poor response continued, the treatment was intensified with high-dose chemotherapy with stem-cell rescue as step 2. Overall, 99% of all patients with metastatic testicular NSGCT in the population were included in the protocol. Median follow-up was 8.2 years. Seventy-seven percent of the patients were treated with BEP alone; 18% received intensification step 1%, and 5% received intensification step 2. Grouped according to International Germ Cell Consensus Classification, 10-year overall survival was 94.7% in good-prognosis patients, 90.0% in intermediate-prognosis patients, and 67.4% in poor-prognosis patients. With detailed treatment protocols and a dedicated collaborative group of specialists, treatment results comparable to those reported from large single institutions can be achieved at national level. With the treatment principles used in Swedish-Norwegian Testicular Cancer Group study SWENOTECA IV, the survival of intermediate-prognosis patients is remarkable and close to that of good-prognosis patients.