OBJECTIVE: We sought to determine the accuracy of cancer registry data regarding the human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) status of patients with non-Hodgkin's lymphoma (NHL). METHODS: We used the population-based San Diego/Orange County cancer registry to identify 392 patients with HIV-related NHL diagnosed 1994-1999. After matching for age, sex, race, period of NHL diagnosis, and hospital type, we were able to find 324 corresponding patients among the remaining 4,863 NHL patients diagnosed 1994-1999 (who did not have HIV infection according to cancer registry records). We sought to review these patients' charts at 41 hospitals with 15 separate institutional review boards to determine if the HIV serostatus from the cancer registry was correct. We performed a forward conditional multivariate logistic regression to determine characteristics associated with a false positive HIV status. RESULTS: The false positive rate was 8% while the false negative rate was 3%. The positive predictive value was 93% while the negative predictive value was 97%. Compared to correctly identified patients, false positives were more likely to be > or =50 years old, female, and treated with chemotherapy and less likely to be single with high grade or extranodal disease. CONCLUSION: Using cancer registry data to identify AIDS-related NHL is a valid research practice.