Little is known about the costs of treating HIV-infected children in Africa. However, this is one of the factors that must be taken into account when assessing the cost-effectiveness of strategies aimed at reducing the transmission of HIV from mother to child. The aim of this study was to estimate the direct costs of the treatment of African children born to HIV-infected mothers and the additional costs of treating those children who are themselves infected with the virus. We assessed the direct costs of care for a sample of children born in 1996 to HIV-positive mothers participating in a clinical trial to evaluate the efficacy of administering a short course of zidovudine to the mother in the peri-partum period, in Abidjan, Ivory Coast (DITRAME ANRS 049a). We systematically reviewed the medical records of these children and recorded drug prescriptions, clinical investigations, consultations with medical specialists, hospital admissions and transportation costs during their first year of life. This study included 78 children, 15 of whom were HIV-positive. The mean cost of treatment was 1,671 FF (254 Euros) per child-year for infected children, 709 FF (108 Euros) more than the mean cost of treatment for HIV-negative children born to HIV-positive mothers. Thus, HIV infection resulted in a 74% increase in treatment costs. The mean cost of a drug prescription was 50 FF (7.6 Euros), and could have been halved if only generic drugs had been prescribed. This study was limited to the direct costs of pediatric HIV infection and did not take into account the cost of health service provision in Ivory Coast or the indirect costs for the family. These results were obtained in the context of a prospective clinical trial within a system providing free and unlimited access to health care. In a city where the mean salary of a civil servant is 900 FF (137 Euros) per month, the expenditure necessary to pay for the basic care of one HIV-infected child is high. Health-care services in sub-Saharan Africa should make more use of generic drugs and pediatric HIV infection provides a clear example of the benefits to be obtained by such a rational strategy for the use of scarce health resources.