Pulmonary complications following orthotopic liver transplantation (OLT) were prospectively evaluated in 18 individuals transplanted at the New England Deaconess Hospital. Of sixteen patients who survived the immediate postoperative period, 12 (75%) sustained a pulmonary complication. Of these complications, 64% were noninfectious--whereas 22% were infectious, and 14% probably infectious. Six of eight documented infections were caused by viruses of the herpes group. In four cases of viral pneumonitis other pulmonary pathogens were isolated (fungi-3, protozoan-1, bacteria-1). Unlike noninfectious complications, pulmonary infections were associated with a fatal outcome in five of six patients who died after OLT. Pulmonary complications are frequent and serious occurrences after OLT, and contribute to both the morbidity and mortality of this procedure. Compared with pulmonary complications seen after transplantation of other organs, OLT was associated with a higher proportion of noninfectious complications but a similar spectrum of pulmonary infections.