The seroprevalence of HIV-1 and in-patient mortality in children with common pediatric illnesses was studied. Between October 1990 and July 1991 at the Department of Paediatrics and Child Health, University Teaching Hospital (UTH), Lusaka, Zambia, mothers of all pediatric admissions were interviewed and counselled for enrollment of their children into the study. Of a total of 1323 children seen, 1266 children (600 female and 666 male) were enrolled into the study. Pneumonia (28 per cent), malaria (24 per cent), malnutrition (18 per cent), and diarrhoea (10 per cent) constituted over 80 per cent of the total admission diagnoses. Tuberculosis (5 per cent) was the fifth commonest cause of admission (61 out of 1266 children). A total of 354 out of the 1266 (28 per cent) children were found to be seropositive for HIV-1 compared to a seroprevalence rate of 9 per cent in children attending accident and emergency for traumatic injuries (P=0.001). High HIV-1 seroprevalence rates were found in children with tuberculosis (69 per cent), malnutrition (41 per cent), pneumonia (28 per cent). and diarrhoea (24 per cent). The overall mortality in hospital among HIV-seropositive children (19 per cent) was significantly higher than those who were HIV-seronegative (9 per cent) (P = < 0.0001).