For the purpose of surveillance of the acquired immunodeficiency syndrome (AIDS) in developing countries, the World Health Organization (WHO) has recommended criteria for the clinical case definition of AIDS in adults and children. In a preliminary examination of children in Zambia a number of patients with obvious AIDS did not fit the published WHO case definition for paediatric AIDS. Based on this the Zambia National AIDS Surveillance Committee designed local criteria for the clinical case definition of paediatric AIDS. We compared the Zambian criteria with the WHO criteria for the diagnosis of paediatric AIDS by studying 134 consecutively admitted children to one of the paediatric wards at the University Teaching Hospital in Lusaka. Twenty-nine of the patients were HIV-1 seropositive and 105 were HIV-1 seronegative. Among the 29 HIV-seropositive patients, the Zambian criteria identified 23, and the WHO criteria identified 20 children as having AIDS. The 105 HIV-seronegative children were classified as having AIDS in 9 cases by the Zambian criteria and in 38 cases by the WHO criteria. These results give the Zambian criteria for the diagnosis of AIDS a sensitivity of 79.3%, a specificity of 91.4% and a positive predictive value of 86.8% compared to a sensitivity of 69%, specificity of 64% and a positive predictive value of 38% for the WHO criteria. The current WHO criteria are inadequate for the diagnosis of paediatric AIDS. The need to refine the WHO criteria for the diagnosis of paediatric AIDS is discussed.