Long-term cancer risks are uncertain in HIV-infected persons, particularly those using highly active antiretroviral therapy (HAART). Timely, population-based surveillance of HIV-associated malignancies in the United States has been challenging because of various data inadequacies. Cancer registries represent a resource for this surveillance, if uncertainties around accurate differentiation of HIV-associated and unassociated cancers can be resolved. To inform the utility of cancer registry data for classifying and monitoring HIV-associated cancers, the completeness and quality of cancer registry-available information about patient HIV status was assessed. For all 10,126 non-Hodgkin lymphomas (NHLs), 1497 Hodgkin lymphomas (HLs), and 895 anal cancers reported to the Greater San Francisco Bay Area registry during 1990-1998, 6 indicators of patient HIV status were retrieved from 2 cancer registry-available sources (cancer registry records, death records) and from linkage with the California AIDS registry. Cross-tabulations were used to examine the distributions of patients with evidence of positive HIV status by indicator and source. Together, 5 cancer registry-available HIV indicators identified 25% more presumed HIV-positive NHL patients and nearly 50% more HL and anal cancer patients than were detected by AIDS registry linkage. Eighty-three percent of NHL patients and at least half of HL and anal cancer patients were identified by multiple sources of HIV indicators, and most individual indicators agreed acceptably with others. However, optimal strategies for classifying HIV-associated patients differed by cancer site. At least in this region, cancer registry data represent a useful resource for monitoring HIV-associated lymphomas and anal cancer and may offer benefits over linkage-based means in the age of HAART.