Adjuvant immune checkpoint inhibitor therapies have radically altered the treatment landscape for renal cell carcinoma and urothelial carcinoma. However, studies have reported negative data regarding adjuvant immune checkpoint inhibitor therapies. Thus, this study aimed to assess the role of adjuvant immune checkpoint inhibitor therapy for both renal cell carcinoma and urothelial carcinoma. A systematic review and network meta-analysis were conducted in compliance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. Multiple databases were searched for articles published as of February 2023. Studies were deemed eligible if they evaluated disease-free survival in patients with renal cell carcinoma and urothelial carcinoma receiving adjuvant immune checkpoint inhibitor therapy. Five studies met the inclusion criteria. In a network meta-analysis, pembrolizumab was shown to be the most effective regimen for patients with renal cell carcinoma, whereas nivolumab was found to be the most effective regimen for patients with urothelial carcinoma. Additionally, these results were consistently observed in a sub-analysis of the T stage. The present analysis provides findings that support the usefulness of adjuvant nivolumab therapy in urothelial carcinoma and adjuvant pembrolizumab therapy in renal cell carcinoma, in agreement with the currently available guidelines. However, the caveat is that the randomized controlled trials included in this analysis differed in important respects despite being similar in study design. Therefore, with these differences in mind, care needs to be taken when selecting patients for these immune checkpoint inhibitor therapies to maximize their benefits.© 2023 The Japanese Urological Association.