Clinicopathologic studies of children who die of acute lower respiratory tract infections: mechanisms of death. Clinicopathologic correlations for 71 cases of fatal pneumonia in children were determined. The mechanism of death for these patients was multifactorial. Severe pneumonia alone accounted for 11 deaths (15.5%). Pneumonia associated with sepsis occurred in 42 children (59.2%). Heart failure (8.5%), hypovolemia (4.2%), and nosocomial infection (12.6%) were also seen in children with fatal acute lower respiratory tract infection. Extensive consolidation, squamous metaplasia, and hyaline membranes were present in the lungs of these children. Patients with severe disease must receive, in addition to antibiotics for acute episodes, individualized intensive respiratory and supportive care. Since these types of care are not available in poor communities, vaccination against measles and vitamin A supplementation for malnourished children may ameliorate the conditions that appear to predispose these children to severe or fatal disease. 