BACKGROUND Cytomegalovirus infection threatens pulmonary allograft survival and function. This retrospective study details the experience of ganciclovir prophylaxis against cytomegalovirus infection and its sequelae. METHODS Eight-nine lung and heart-lung transplant recipients with positive cytomegalovirus serology were analyzed. The 37 recipients who underwent transplantation before September 1989 received no prophylaxis. The 52 subsequent recipients received ganciclovir prophylaxis. RESULTS Thirty-six non-prophylaxed versus 42 prophylaxed patients had cytomegalovirus events with cumulative incidences of 100% and 86% (p < < 0.01), and median onsets of 37 +/- 21 versus 85 +/- 35 days, respectively (p < < 0.01); 22 non-prophylaxed versus 27 prophylaxed patients had cytomegalovirus pneumonitis with cumulative incidences of 60% and 55% (p < < 0.01), and median onsets of 34 +/- 14 and 84 +/- 26 days, respectively (p < < 0.01). Respiratory failure caused by cytomegalovirus pneumonitis developed in nine of the non-prophylaxed versus two of the prophylaxed patients (p < < 0.01). The significant estimated survival benefit in patients who received prophylaxis (p = 0.04) was not apparent when reanalysis was performed after exclusion of patients with respiratory failure (p = 0.36). Ganciclovir prophylaxis produced a significant delay in the development of obliterative bronchiolitis with a median time to onset of 1072 +/- 280 days versus 432 +/- 189 days for the non-prophylaxis cohort (p < < 0.01). CONCLUSIONS Ganciclovir prophylaxis (1) improves recipient survival by reducing the severity of disease and essentially eliminating respiratory failure caused by cytomegalovirus pneumonitis, (2) reduces the incidence and delays the onset of cytomegalovirus events and pneumonitis, and (3) delays the onset of obliterative bronchiolitis.