Severe anemia is one of the major complications of malaria in Africa. We studied 2 populations, one in a village and the second in a periurban area in Mali, to understand the preventable factors in the disease. The 2 correlates of disease were parasitemia above 100 000 parasitized red blood cells per microliter (0.1 x 10(12)/L) and a low baseline hemoglobin level. All cases of moderate to severe anemia occurred in children under 3.2 years of age. Raising the baseline hemoglobin level and lowering peak parasitemia in infants and young children may reduce the incidence of severe anemia resulting from malarial infection.