Background: We aim to investigate non-cancer cause of death in adults within 2 years after initial diagnosis of mGU cancers including bladder cancer (BC), kidney cancer (KC), and prostate cancer (PC). Methods: Surveillance, Epidemiology, and End Results (SEER) database (2004-2020) was searched to obtain data on death caused by cardiovascular diseases (CVD), kidney diseases (KD), respiratory diseases (RD), liver diseases (LD), diabetes mellitus (DM), and sepsis in adults (>20y of age) diagnosed with mGU cancers. Standardized mortality ratios (SMRs) with 95% confidence interval (CI) were calculated within 2y of initial diagnosis. SMR was defined as the observed deaths from each category divided by the expected number of deaths in the age-matched US population for the same period. SMR >1 indicated increased while <1 indicated decreased mortality. Stratification factors included age (<50y, 50-70y, >70y), race (White, Black, Asian/Pacific Islander), ethnicity (Hispanic, non-Hispanic), chemotherapy, and radiotherapy. Results: This study including 77,246 mGU cancer patients showed that the greatest risk of early death was observed to be caused by sepsis (SMR: 4.21, 95% CI: 3.64-4.84) followed by CVD (1.70, 1.62-1.80), KD (1.58, 1.31-1.90), LD (1.58, 1.16-2.09), DM (1.56, 1.32-1.82), and RD (1.38, 1.22-1.56). Patients aged <50y observed the highest risk of mortality caused by sepsis (61.76, 30.83-110.5) followed by KD (28.06, 9.11-65.48) and CVD (5.63, 3.60- 8.84). However, patients aged 50-70y were more likely to die by RD (2.47, 1.94-3.09) and LD (2.01, 1.38-2.82). The results were consistent for Black patients; sepsis (6.59, 5.04-8.46) followed by RD (2.01, 1.41-2.78) and KD (1.64, 1.04-2.46). Asian/Pacific Islanders were more likely to die from CVD (2.52, 2.13- 3.00) and DM (2.21, 1.21-3.71). Hispanics were more likely to die from LD (3.11, 1.66-5.32) and non-Hispanics from sepsis (4.28, 3.68-4.96). This risk of death due to sepsis was increased with chemotherapy (7.06, 5.22-9.33) and radiotherapy (4.92, 3.58-6.61). Detailed results are available in Table. Conclusions: Sepsis remained the leading cause of early non-cancer-deaths in mGU cancers consistently across all subgroups. Younger adults were more likely to die from CVD and KD, Black patients from RD, and Hispanics from LD.