The prevalence and age distribution of anemia and malaria among Yanomami Amerindians undergoing sociocultural assimilation are described. Anemia and malaria proportions were determined in 103 individuals randomly selected from 515 villagers in Mavaca in the southern Venezuelan Amazon. The age and sex distribution reflected that of the entire village cluster. Anemia (hematocrit less than World Health Organization/Centers for Disease Control and Prevention reference values) was found in 91% of the study population. As a group, adults (> or = 15 years old) had the highest proportion of anemia (P=0.037). Adult females had lower mean hematocrit values than adult males (P=0.013). The anemia was predominantly hypochromic and microcytic (62%), a finding that could suggest a diagnosis of iron deficiency in the absence of known hereditary hemoglobinopathies in these Amerindians. Malaria was diagnosed in 14% overall. Children (< 10 years old) displayed the highest proportion of Plasmodium falciparum (17%) and P. vivax (14%) parasitemia, splenomegaly (94%), and fever (34%) (P=0.059, 0.039, 0.005, and 0.008, respectively). The high proportions of anemia and splenomegaly observed in the survey may be used as indicators of inadequately controlled malaria in this community. Further studies to assess the epidemiology of risk factors for the high prevalence of anemia, and predominance of P. falciparum infections in the area are urgently needed.