Summary:In Dar es Salaam, Tanzania, 200 children with severe malnutrition and controls matched for age, sex, and area of residence were screened for serological evidence of infection with the human immunodeficiency virus type 1 (HIV-1) over 5 months in 1988. The prevalence of HIV-1 antibodies in the malnourished group was 25.5% (51 of 200) compared with 1.5% (three of 200) in the controls. The seroprevalence rate was equally high in malnourished children above the age of 18 months (26 of 102; 25.5%), as in those below this age (25 of 98; 25.5%). The prevalence rate was higher in children with marasmus (38.2%) as compared to children with marasmic-kwashiorkor (12.3%) or kwashiorkor (12.2%). The prevalence of clinical features known to be associated with AIDS was higher in the HIV seropositive malnourished children as compared to the seronegative children. The modified World Health Organization clinical case definition of AIDS in children was also evaluated and found to have a low sensitivity and positive predictive value (62.8 and 57.1%, respectively) but a fairly high specificity (83.9%). It is recommended to routinely rule out HIV infection in malnourished children, especially those with marasmus.