Objective: HIV-infected people and elderly people have higher cancer risk, but the combined effects of aging and HIV are not well described. We aimed to evaluate the magnitude of cancer risk in the HIV-infected elderly population. Design: We conducted a case-cohort study including a 5% sample of U.S. Medicare enrollees and all cancer cases aged at least 65 in linked cancer registries. Methods: HIV was identified through Medicare claims. Among the HIV-infected, absolute cancer risk was calculated accounting for the competing risk of death. Associations between HIV and cancer were estimated with weighted Cox regression adjusting for demographic characteristics. Results: Among 469 954 people in the 5% sample, 0.08% had an HIV diagnosis. Overall, 825 776 cancer cases were identified in cancer registries. Over 5 years, 10.1% of the HIV-infected elderly developed cancer, the most common diagnoses comprising lung (5-year cumulative incidence=2.2%), prostate (2.7%, among men), and colorectal cancer (0.9%), and non-Hodgkin lymphoma (0.8%). HIV was strongly associated with incidence of Kaposi sarcoma [adjusted hazard ratio (aHR)=94.4, 95% confidence interval (95%CI)=54.6-163], anal cancer (aHR=34.2, 95%CI=23.9-49.0) and Hodgkin lymphoma (aHR=6.3, 95%CI=2.8-14.3). HIV was also associated with incidence of liver cancer, non-Hodgkin lymphoma and lung cancer (aHR=3.4, 2.6, and 1.6, respectively). Conclusion: In the elderly, HIV infection is associated with higher risk for many cancers, although some associations were weaker than expected, perhaps reflecting effects of non-HIV pathways on cancer development. Due to the effects of HIV and aging, the HIV-infected elderly have a sizeable absolute risk, highlighting a need for cancer prevention.