To study the role of single agent carboplatin chemotherapy in patients with metastatic seminoma based on the data from two randomised trials. In subgroup analyses in patients with different disease characteristics, the outcome treated with either single agent carboplatin or cisplatin-based combination chemotherapy was compared. Individual patient data from two randomised European trials involving patients with metastatic seminoma were gathered. The primary endpoint for all analyses was progression-free survival. The source data of 361 patients, 184 treated with cisplatin-based combinations and 177 treated with carboplatin single agent therapy, were entered into the analysis. Patient characteristics were comparable among the cisplatin-based and the carboplatin single agent treated patient groups with lymph nodes and lungs being the most frequent metastatic sites in 92 and 8% of patients, respectively. Overall, patients treated with single agent carboplatin had an inferior 5-year overall (89 and 94%; P=0.09) and progression-free survival rate (72 and 92%; P< 0.0001) compared with patients receiving cisplatin-based combinations. For all investigated subgroups (based on age, prior radiation therapy, metastatic sites), carboplatin single agent therapy was found to be inferior to cisplatin-based combination chemotherapy. In conclusion, carboplatin single agent therapy cannot be recommended as standard treatment for any patient subgroup with advanced metastatic seminoma and cisplatin-based combination regimens remain the standard of care.