Between June 1988 and February 1993, combined heart-lung transplantation was performed in 30 children and adolescents aged 3.6 to 18.6 years (mean, 12.2 years) at The Hospital for Sick Children in London. Original diagnoses included cystic fibrosis (n = 25), Eisenmenger's syndrome (n = 4), and chronic graft-versus-host disease of the lung (n = 1). Posttransplantation maintenance immunosuppression comprised a triple regimen, with methylprednisolone and antithymocyte globulin given perioperatively and for episodes of allograft rejection. Actuarial survival was 63% (95% confidence interval: 42%-78%) at 1 year and 48% (95% confidence interval: 27%-66%) at 3 years. Obliterative bronchiolitis has been diagnosed in 13 patients (43%). Actuarial freedom from obliterative bronchiolitis in survivors was 76%, 59%, and 37% at 12, 24, and 36 months after transplantation, respectively. Recipients in whom obliterative bronchiolitis developed within the first year (n = 6) had more episodes of pulmonary rejection during the first 6 months after transplantation (mean, 5.7 episodes per patient) than those in whom "premature" obliterative bronchiolitis did not develop (mean, 3.2 episodes per patient). Infection of the pulmonary allograft was implicated to a lesser extent in predisposing to obliterative bronchiolitis. At 2, 3, and 6 months, tracheal stenosis developed in three patients, all of whom died with obliterative bronchiolitis within 10 months of transplantation. Noncompliance with therapy was considered a contributory factor in producing obliterative bronchiolitis in four adolescent recipients. The high incidence of obliterative bronchiolitis observed in this pediatric cohort may have a multifactorial cause.