Randomised trials can provide high-level evidence to inform treatment decisions. Since their quality in respiratory medicine is largely unknown, we assessed the quality of a large set of chronic obstructive pulmonary disease (COPD) trials. As a marker of trial quality, we assessed the procedure and concealment of random allocation, and the conduct of an intention-to-treat-analysis in 344 randomised trials published between 1957 and 2006. We used ordered logistic regression to assess the association between trial quality and type of intervention, type of journal, journal impact factor and year of publication. 257 (75%) trials assessed pharmacological and 87 (25%) assessed nonpharmacological interventions. The generation of appropriate randomisation was reported in 27.0% of the trials, concealment of random allocation in 11.6% and an intention-to-treat analysis in 21.8% of trials. Significantly higher quality was found in trials on nonpharmacological interventions (OR 2.49, 95% CI 1.56-3.99), and in trials published in general medical journals (versus specialised journals; OR 2.25, 95% CI 1.30-3.90) and after 2000 (versus 1957-2000; OR 2.28, 95% CI 1.45-3.58). The association of quality with a high impact factor was of borderline significance (p = 0.06). The quality of many COPD trials is low but tends to become better since the adoption of the CONSORT (Consolidated Standards of Reporting Trials) statement.