Background: Adjuvant chemotherapy is used in stage I testicular seminoma. We have reported a risk-adapted strategy of 2 cycles of cisplatin/etoposide (EP) in 64 patients with age < 34 and/or tumor diameter > 4cm) (Bamias et al, Urology 2007), resulting in no relapses over a median follow up of 5 years. Following the establishment of adjuvant carboplatin as a standard, we adopted this treatment for all patients with stage I seminoma. We report our 8-year experience and compare these results with our previous EP strategy. Methods: Patients with stage I seminoma, treated with 2 cycles of carboplatin AUC 6 and a minimum follow up of 1 year after chemotherapy were selected. All patients consented for the use of their medical information and the analysis was approved by the centers involved. Survival functions were presented using Kaplan-Meier curves. The log-rank test was used to test for survival differences across different categories. Results: 137 patients (Median age: 34; Age<34: 49%, tumor diameter>4cm: 42%; rete testis invasion: 24%), treated between 11/2003-12/2011 were selected. During a median follow up of 4 years, there were 5 relapses (5-y relapse rate [RR]: 97% [SE: 2%]): retroperitoneal lymph nodes (n=4) and isolated brain (n=1). All patients with relapse had tumor diameter > 4cm and/or age < 34. No relapse was associated with rete testis invasion. Patients with at least 1 of the above risk factors (n=94) had a significantly higher relapse rate compared with a similar population (n=64) treated with 2 cycles of adjuvant EP: 5-y RR was 95% (SE: 2%) vs.100% (SE 0%), (p=0.033). All relapsed patients were treated with BEP chemotherapy and are currently alive with no evidence of relapse. Neutropenia and nausea/vomiting were less frequent with carboplatin than with EP (11% vs. 36% and 15% vs. 65%). Conclusions: Our analysis confirms the association of age and tumor diameter with relapse in stage I seminoma treated with adjuvant carboplatin. Although adjuvant carboplatin in patients with age<34 and/or tumor diameter> 4 cm is associated with higher RR than EP, the prognosis of these patients is excellent with salvage chemotherapy and, therefore, the use of less toxic treatment is justified.