This study assesses trends and disparities in next-generation sequencing (NGS) testing among patients with metastatic prostate cancer (mPC) and advanced urothelial carcinoma (aUC). Using a retrospective cohort study design, data from 11,927 patients with mPC and 6,490 patients with aUC were analyzed. The primary outcomes were NGS testing rates by year of diagnosis and time to NGS testing, considering death as a competing risk. Social determinants of health, including race, ethnicity, socioeconomic status (SES), region, insurance type, and sex, were evaluated. Results showed that NGS testing rates increased over time, but disparities persisted. Black patients and those with low SES were less likely to undergo NGS testing, regardless of the cancer type. Patients with aUC living in the South were more likely to undergo testing. The study highlights the need to improve access to NGS testing to address health disparities and enhance personalized treatment options for patients with mPC and aUC.This study assesses trends and disparities in next-generation sequencing (NGS) testing among patients with metastatic prostate cancer (mPC) and advanced urothelial carcinoma (aUC). Using a retrospective cohort study design, data from 11,927 patients with mPC and 6,490 patients with aUC were analyzed. The primary outcomes were NGS testing rates by year of diagnosis and time to NGS testing, considering death as a competing risk. Social determinants of health, including race, ethnicity, socioeconomic status (SES), region, insurance type, and sex, were evaluated. Results showed that NGS testing rates increased over time, but disparities persisted. Black patients and those with low SES were less likely to undergo NGS testing, regardless of the cancer type. Patients with aUC living in the South were more likely to undergo testing. The study highlights the need to improve access to NGS testing to address health disparities and enhance personalized treatment options for patients with mPC and aUC.