Screening for oral leukoplakia, an oral cavity cancer (OCC) precursor, could lead to earlier detection of OCC. However, the progression rate from leukoplakia to OCC and the benefits of leukoplakia screening for improving OCC outcomes are currently unclear. We conducted a case-cohort study of U.S. adults ages ≥65 years in the Surveillance, Epidemiology, and End Results (SEER)-Medicare linkage. We identified leukoplakia diagnoses through Medicare claims, and OCC diagnoses through SEER cancer registries. Weighted Cox regression was used to estimate leukoplakia associations with OCC incidence, and the absolute OCC risk following leukoplakia diagnosis was calculated. Among OCC cases, we compared OCC stage and OCC survival between cases with a prior leukoplakia diagnosis versus those without prior leukoplakia. Among 470,266 individuals in the SEER-Medicare subcohort, 1,526 (0.3%) had a leukoplakia diagnosis. Among people with leukoplakia, the cumulative OCC incidence was 0.7% at 3 months and 2.5% at 5 years. OCC risk was most increased <3 months after leukoplakia diagnosis (HR, 115), likely representing the diagnosis of prevalent cancers. Nonetheless, risk remained substantially increased in subsequent follow-up [HR ≥ 3 months, 24; 95% confidence interval (CI), 22-27; HR ≥ 12 months, 22, 95% CI, 20-25]. Among OCC cases (N = 8,927), those with prior leukoplakia were less likely to be diagnosed at regional/distant stage (OR, 0.36; 95% CI, 0.30-0.43), and had lower mortality (HR, 0.74; 95% CI, 0.65-0.84) when compared with OCC cases without a prior leukoplakia. Individuals with leukoplakia have substantially elevated risk of OCC. Lower stage and better survival after OCC diagnosis suggest that leukoplakia identification can lead to earlier OCC detection and reduced mortality.