A multiinstitutional study of 307 heart transplant recipients was carried out to determine the clinical, radiographic, and prognostic characteristics, the incidence, and the etiology of pneumonias in the first year after transplantation. There were 21.1 cases of pneumonia per 100 heart transplantations. Seventy-five percent of the cases occurred in the first trimester. Eighty-two causal agents were identified, of which 60% were opportunistic, 25% were nosocomial, and 15% were community-acquired. The most frequent isolates were cytomegalovirus (20), Aspergillus species (13), and Pneumocystis carinii (11). Hemoptysis occurred more frequently in aspergillus pneumonias than in other pneumonias (54% vs. 6%, respectively; P < .05); aspergillus pneumonia was the only type of pneumonia during which cavitated nodules were noted on thoracic radiographs. The overall mortality rate was 30.8%; the independent factors of a poor prognosis were aspergillus infection (relative risk [RR], 7.4; 95% confidence interval [CI], 5.8-9.1) and bilateral pulmonary infiltrates (RR, 10; 95% CI, 8.5-11.4).