This study examines trends and disparities in next-generation sequencing (NGS) testing among patients with metastatic prostate cancer (mPC) and advanced urothelial carcinoma (aUC). The study analyzed data from 11,927 patients with mPC and 6,490 patients with aUC, collected from a nationwide electronic health record database. The primary outcomes were the rate of NGS testing and the time to NGS testing, considering death as a competing risk. Disparities in NGS testing were assessed based on race/ethnicity, socioeconomic status (SES), region, insurance type, and sex (for aUC). The NGS testing rate increased over time for both mPC and aUC. However, Black patients, those with low SES, and those with Medicaid or Medicare insurance were less likely to undergo NGS testing. In the mPC cohort, the NGS testing rate increased from 19.0% in 2015 to 27.1% in 2022. In the aUC cohort, the rate increased from 14.1% in 2015 to 46.6% in 2022. Despite these increases, the majority of patients in both cohorts did not undergo NGS testing. The study highlights significant disparities in access to NGS testing based on social determinants of health. These disparities suggest that while NGS testing is available, many patients, particularly those from disadvantaged backgrounds, do not have access to it. The findings emphasize the need to improve access to quality healthcare and address disparities in genomic testing. The study also underscores the importance of policies that support equitable access to NGS testing, such as the Medicare National Coverage Determination, which categorizes NGS as an essential diagnostic tool for patients with advanced or metastatic cancer.This study examines trends and disparities in next-generation sequencing (NGS) testing among patients with metastatic prostate cancer (mPC) and advanced urothelial carcinoma (aUC). The study analyzed data from 11,927 patients with mPC and 6,490 patients with aUC, collected from a nationwide electronic health record database. The primary outcomes were the rate of NGS testing and the time to NGS testing, considering death as a competing risk. Disparities in NGS testing were assessed based on race/ethnicity, socioeconomic status (SES), region, insurance type, and sex (for aUC). The NGS testing rate increased over time for both mPC and aUC. However, Black patients, those with low SES, and those with Medicaid or Medicare insurance were less likely to undergo NGS testing. In the mPC cohort, the NGS testing rate increased from 19.0% in 2015 to 27.1% in 2022. In the aUC cohort, the rate increased from 14.1% in 2015 to 46.6% in 2022. Despite these increases, the majority of patients in both cohorts did not undergo NGS testing. The study highlights significant disparities in access to NGS testing based on social determinants of health. These disparities suggest that while NGS testing is available, many patients, particularly those from disadvantaged backgrounds, do not have access to it. The findings emphasize the need to improve access to quality healthcare and address disparities in genomic testing. The study also underscores the importance of policies that support equitable access to NGS testing, such as the Medicare National Coverage Determination, which categorizes NGS as an essential diagnostic tool for patients with advanced or metastatic cancer.