The World Health Organization (WHO) in 1993 developed the integrated management of childhood illness (IMCI) draft algorithm which offers guidelines upon the diagnosis and treatment of acute respiratory infections, diarrhea, malaria, measles, ear infections, and malnutrition, as well as immunization status. During a 14-month study period, 1795 children aged 2 months to 5 years were enrolled in the study from the outpatient pediatric clinic of Siaya District Hospital in western Kenya, of whom 52% were male and the median age was 13 months. 51% of the children complained of having fever, 22% of having a cough, and 11% of having diarrhea. 86% of the main complaints were directly addressed by the IMCI algorithm. 1210 children had Plasmodium falciparum infection and 1432 met the WHO definition for anemia. The sensitivities and specificities for classification of illness by a minimally trained health worker using the IMCI algorithm compared to diagnosis by the physician were: pneumonia, 97% sensitivity and 49% specificity; dehydration in children with diarrhea, 51% and 98%, respectively; malaria, 100% and 0%; ear problem, 98% and 2%; nutritional status, 96% and 66%; and need for referral, 42% and 94%. Detection of fever by placing a hand upon the forehead was 91% sensitive and 77% specific. Considerable clinical overlap was observed between pneumonia and malaria, and between malaria and malnutrition. Study findings led to some changes in the IMCI algorithm.