Data from a population-based survey, conducted in the northeast of Brazil, were used to examine the association between acute respiratory infection (ARI) and malnutrition in children under 5 y of age. Current and past malnutrition were associated with acute lower respiratory infection (ALRI), even after adjusting for potential confounders (odds ratio: 2.03; 95% confidence interval: 1.20-2.43). Decreasing malnutrition along with timely and proper treatment of ARI may improve children's health in developing countries.