Background: The SWENOTECA group has since 1998 offered patients with clinical stage I (CSI) nonseminoma (NSGCT) treatment based on a risk-adapted approach. Patients with lymphovascular invasion (VASC+) were recommended one course of adjuvant chemotherapy (ACT) with bleomycin, etoposide and cisplatin (BEP). Patients without lymphovascular invasion (VASC-) had the choice between one course of adjuvant BEP or active surveillance. Methods: From 1998-2010, 491 patients with CSI NSGCT received one course of adjuvant BEP. Following histopathological evaluation 247 patients were classified as VASC+, 239 as VASC- and five patients had uncertain VASC status. All patients were included into a prospective, community-based, multicenter SWENOTECA management program. Initial results from patients treated during 1998-2005 have earlier been reported. We now report the mature data, expanded with patients treated during 2005-2010. Results: The median follow-up was 8.0 years. Eleven relapses were observed. After one course of adjuvant BEP 2.3% of patients relapsed. In regard to VASC status 3.4% of VASC+ and 1.3% of VASC- patients relapsed. The latest relapse was detected 3.3 years after ACT. Ten patients have died, only one due to testicular cancer. The 5 and 10-year overall survival rates were 98.9% and 96.8%, respectively. The 5 and 10-year disease-specific survival rates were 100% and 99.6% respectively. Conclusions: One course of adjuvant BEP reduces the risk of relapse in CSI NSGCT with over 90%. These mature results confirm our earlier results on one course of adjuvant BEP. There is no evidence of late relapses, or chemotherapy-resistance in relapses following ACT. To detect relapses, a follow-up of five years is sufficient.