Background: Significant advances in the management of VTE in cancer have led to a recent ASCO clinical practice update for VTE prophylaxis and treatment in patients with cancer. Genitourinary (GU) cancers (including bladder, kidney, prostate, testicular) have a high incidence of VTE, but also frequent bleeding complications, and it is not clear if patients with GU cancers are adequately represented in studies of VTE prophylaxis. We sought to determine the frequency of inclusion of patients with GU cancers in prospective studies of VTE prophylaxis. Methods: A systematic review of the literature using MEDLINE (inception to January 2020) was conducted. We included randomized controlled trials that compared thromboprophylaxis to placebo or best supportive care in patients with an established diagnosis of cancer. Observational studies, case series, and case reports were excluded. The primary outcome was proportion of patients with GU malignancies included within the trials. Results: A total of 137 articles were identified under the original search and 7 underwent full text review. A total of 6066 patients were included in 7 thromboprophylaxis trials, of which only 119 (2.0%) had a defined GU malignancy (Table). Given the heterogeneity of the GU cancers represented in each study, and the small numbers of patients included with GU cancers, a patient-level meta-analysis among GU patients in this population was not performed. Conclusions: In spite of the high risk for VTE in GU cancers, in particular bladder and testicular cancer, GU cancers are underrepresented in prospective randomized trials investigating VTE prophylaxis. To ensure appropriate decision making for each individual patient, future prospective trials must ensure adequate representation of patients with GU cancers to better understand the potential role for VTE prophylaxis in this high-risk population.