The seroprevalence of measles (rubeola) antibody in 619 human immunodeficiency virus (HIV)-infected adults was determined by a standard ELISA. Risk factors for a lack of antibody and presumed susceptibility to measles were examined. Whereas overall, 9.8% of patients (60) were found to lack antibody, 17.8% of those born within the United States in 1957 or later were antibody-negative. Multivariate analysis showed that absence of measles antibody was significantly associated with younger age (born in 1957 or later) (odds ratio [OR], 8.15; 95% confidence interval [CI], 3.7-21.5; P < .0001) and birth within the United States (OR, 4.72; 95% CI, 1.7-19.7; P = .0045). Neither minority status, stage of HIV infection, CD4 cell count, nor a history of opportunistic infection bore any relationship to the presence of antibody. While progression of HIV disease does not affect measles serostatus, younger HIV-infected patients, especially those born in the United States in 1957 or later, are at the greatest risk for measles.