Clinical trials are integral to scientific discovery and advancement and can ensure access to standard of care treatments, providing benefits to society and individual participants. However, disparities in clinical trial enrollment persist across vulnerable populations and remain a barrier to achieving equitable cancer care. A major contributor to this disparity may be access and availability to clinical trials, including geographic availability within a logistically reasonable travel area. It is possible that low levels of representation in clinical trials is secondary to low availability to specific groups, and that expanding the availability of trials could improve enrollment rates and representation in trials. For these reasons, we evaluate the association between population-level social determinants of health (SDOH) and county-level urologic cancer clinical trial availability in the United States. Using custom data linkage from ClinicalTrials.gov, Surveillance Epidemiology and End Results (SEER) Registry, and the Centers for Disease Control and Prevention Social Vulnerability Index (SVI), we performed a cross-sectional analysis of county-level clinical trial data, cancer incidence rates, and population-level SDOH. We included Phase 2 and Phase 3 interventional clinical trials from 2007 to 2022 for prostate, kidney, and bladder cancer. The total and cancer-specific number of available clinical trials over the study period were calculated for each county and population-adjusted for 100,000 residents. Counties were stratified into quintiles based on SVI (i.e., least vulnerable to most vulnerable). Population adjusted county-level clinical trial availability and cancer incidence rates were compared across SVI quintiles. Multivariable logistic regression and negative binomial regression analyses were performed to evaluate the association between SVI quintile and clinical trial availability. Across the included urologic cancer types, only 40.8% of counties in the United States had 1 or more clinical trials. Clinical trial availability by urologic cancer type ranged from 41.8% for prostate cancer, 36.6% for bladder cancer and 32.0% for kidney cancer. The mean number of urologic cancer clinical trials per 100,000 residents was 64.4, with the most vulnerable counties having significantly fewer clinical trials compared to the least vulnerable counties (42.7 vs. 132.0, p<0.05). Further, the most vulnerable counties had significantly decreased odds of having any urologic cancer clinical trial (OR 0.31, 95% CI 0.23 – 0.43) and significantly fewer clinical trials (incidence rate ratio (IRR) 0.38, 95% CI 0.27 – 0.54) compared to the least vulnerable counties. These findings were consistent on sub-analysis of each urologic cancer type. Significant geographical disparities in urologic cancer clinical trial availability exist in the United States, with less than half of all counties having any clinical trial for the most common urologic cancers. Further, the most socially vulnerable counties were far less likely to have any clinical trial available, even after adjusting for county population, cancer incidence rates, and presence of a Commission on Cancer accredited hospital.; These counties represent areas of scientifically underserved populations and highlights a potential mechanism to improve representation in studies and outcomes in vulnerable populations with cancer. [ABSTRACT FROM AUTHOR]