Pulmonary function (PF) was studied in 69 consecutive patients with hematologic diseases, with a minimum 5-year (range, 5-13 years) follow-up after allogeneic stem cell transplantation from an HLA-matched sibling. Fifty-six patients (81%) received total body irradiation based myeloablative stem cell transplantation (MT) and 13 (19%) underwent nonmyeloablative stem cell transplantation (NST). Thirty-one patients (45%) developed a late decrease in PF from baseline, 25 with a restrictive and 6 with an obstructive pattern PF abnormality. Twelve patients (17%) were symptomatic, 8 with a severe restrictive PF defect, but none required supplemental oxygen. The incidence of developing a late PF abnormality was comparable in MT (24 of 56) and NST (5 of 13; P = .51). In multivariate analysis, chronic graft-versus-host disease (relative risk, 16) and pretransplantation diffusion capacity for carbon monoxide or forced expiratory volume in the first second <80% predicted were independently associated with a late decrease in PF from baseline (relative risk, 7). Our results indicate that late PF abnormality is common after MT and NST. Patients with a low pretransplantation diffusion capacity for carbon monoxide of or forced expiratory volume in the first second who developed chronic graft-versus-host disease were most severely affected. Longer follow-up is needed to determine whether PF will continue to decrease or reach a plateau and whether more patients with PF abnormality will eventually become symptomatic.