Background: Cancer related thrombosis affects ~20% of all cancer patients. It is our standard practice to refer cancer patients with suspected venous thromboembolism (VTE) to our Cancer Associated Thrombosis (CAT) clinic. Referrals are based on a clinical suspicion of VTE or a Khorana score ≥3. We sought to evaluate the characteristics of patients with genitourinary (GU) cancer referred to the CAT clinic and their association with immunotherapy. Methods: The study population comprised of all cancer patients referred to the CAT clinic with a diagnosis of prostate cancer (Pca), bladder cancer (BC) or renal cell cancer (RCC) from August 1, 2014 to October 15, 2019. Results: Of the 147 patients with GU cancers referred to CAT clinic, 43 had a VTE (14/40 BC, 14/44 RCC, 15/63 PCa). Of which, 83% were DVT, 5% were PE, and 12% had both. The majority had stage 4 disease (98%), no prior clotting history, and ECOG 0-2 (86%). Average BMI was 28.63 and 22 patients had smoking histories (average 11 pack years). Major histology per cancer type were adenocarcinoma (100%) in PCa, 86.7% clear cell in RCC and 85.7% urothelial carcinoma in BC. Lower extremity pain or swelling (67%) was the major reason for referral. Thirty-four of the 43 patients were on active treatment; 7 patients on immunotherapy (average 4.9 months) and 13 patients on chemotherapy (average 2.6 cycles) at the time of VTE diagnosis. Of the chemotherapy regimens, patients were on the combination of gemcitabine with carboplatin (54%), docetaxel (23%), or cabazitaxel (23%). Atezolizumab was the most commonly used immunotherapy agent (57%). Other immunotherapy agents associated were nivolumab (29%) and the combination of ipilimumab with nivolumab (14 %). There was no VTE-related mortality. Conclusions: Our single center experience shows 16% of VTE events in patients with GU cancers were associated with immunotherapy and 33% were associated with cytotoxic chemotherapy. There is a growing body of literature exploring the association between thromboembolic events and immunotherapy. As more patients with GU cancers are treated with immunotherapy, it will be interesting to see how this influences the rate of CAT clinic referral and prevalence rates of VTE.