Summary:To provide an estimate of the seroprevalence of human immunodeficiency virus (HIV) in a representative sample of the U.S. household population, serum samples from participants in the third National Health and Nutrition Examination Survey (NHANES III) were tested for HIV antibody. The testing was performed anonymously on 5,430 individuals 18–59 years old from phase 1 of NHANES III conducted from 1988 to 1991. Twenty-nine individuals were HIV positive. The total weighted prevalence was 0.39%. The population estimate of infected individuals was 547,000, with a 95% confidence interval of 299,000–1,020,000 infected persons. Black participants were four times more likely to be HIV positive than white/other individuals and three times more likely than Mexican Americans. Men were three times more likely to be infected than women. Higher nonresponse to the survey and to phlebotomy was observed in young white men; therefore these data provide a conservative estimate of HIV infection in the general household population. This estimate does not include individuals who do not live in households and who may be at higher risk of infection, such as persons in penal institutions, the homeless, or certain hospitalized patients.