A case-control study was undertaken in 400 children under 5 years of age in South Kerala, India, to identify the risk factors for severe pneumonia. Cases were in-patients with severe pneumonia as ascertained by WHO criteria, while controls were out-patients with non-severe acute respiratory infections. Only four from many probable risk factors emerged as being significant, viz. young age, immunization, delayed weaning, and sharing of bedroom. The significant factors on univariate analysis were parental education, environmental pollution, discontinuation of breastfeeding in young infants, malnutrition, hypovitaminosis A, low birth weight, previous history of severe ARI, unresponsiveness to earlier treatment, and use of non-allopathic medicine. Correction of these factors can probably reduce mortality due to ARI.