We studied long-term pulmonary function testing (PFT) in a retrospective cohort of 6-month survivors of allogeneic marrow transplant (BMT) between 1980 and 1997. Of 593 patients, 73, 71 and 65% had adequate data to assess for obstruction, restriction and diffusion impairments respectively. Over 5 years, mean declines in 1-s forced expiratory volume/forced vital capacity (FEV1/FVC), total lung capacity (TLC) and diffusion were 4, 7 and 17%, respectively. TLC and diffusion tended to subsequently increase. In all, 6, 12 and 35% of patients met criteria for obstruction, restriction and impaired diffusion, respectively. Obstruction was less common in recent transplants (5 vs 15%, P=0.004), while restriction and diffusion impairment rates remained stable. There was significantly greater mortality with obstruction (HR 2.0 (1.04-3.95)), and a nonstatistically significant higher mortality rate with restriction (HR 1.6 (0.95-2.75)), but not with impaired diffusion (HR=0.99 (0.65-1.50)). cGVHD (OR 16.7 (2.2-129.8)) and busulfan (OR 2.9 (1.01-8.24)) were associated with obstruction. Marrow from nonsibling or mismatched donors (OR 4.9 (2.2-10.7)) was associated with restriction. In summary, after BMT, decreased diffusion capacity is common and benign; obstruction has decreased in frequency, is rare without cGVHD, and is associated with mortality; nonsibling and mismatched donor are risk factors for restriction.