In a total of 1,003 children (805 inpatients and 198 outpatients) with acute lower respiratory infections (ALRI), clinical, social, and environmental data were analyzed. The major clinical entities were bronchiolitis, pneumonia, bronchitis, and laryngitis. The first two of these predominated in inpatients; pneumonia and bronchitis were more common in older children, while bronchiolitis was observed in infants. Respiratory rates of > 50/min. were more common in younger children and in cases with bronchiolitis and bronchitis. Retractions showed markedly less age-dependent variations and were present in all severe cases with different clinical diagnoses. Retractions alone or associated with cyanosis were the best indicators for severity of ALRI. Among outpatients, fever and wheezing were more common; inpatients were younger, more frequently malnourished, and from a lower socioeconomic level; family history of chronic bronchitis, crowding, and parental smoking also prevailed in this group. Family asthma and exposure to domestic aerosols was more common among outpatients. Prematurity rate (17 and 15%) of all ALRI cases was twice that of the general pediatric population and a significant difference existed between in- and outpatients under 6 months of age when perinatal respiratory pathologies predominated among inpatients. It is suggested to consider the need for assessing personal, family, and environmental risk factors in addition to clinical signs and symptoms when severe cases of ALRI are evaluated.