UNLABELLED: The aim of this study was to determine the minimal important difference for the six-minute walk distance in people with diffuse parenchymal lung disease. METHODS: Forty-eight subjects (24 idiopathic pulmonary fibrosis) undertook the six-minute walk test before and after an 8-week exercise program. The minimal important difference was calculated using a distribution-based and an anchor-based method. A global rating of change scale was used as the external criterion to judge patients as clinically unchanged or changed. RESULTS: The mean change in six-minute walk distance in improved subjects was 50.0 m, compared to 4.0 m in unchanged subjects and a reduction of 64.3 m in those classified as worse (p<0.001). The receiver operating characteristic curve indicated a cut-off value for meaningful change of 30.5 m (area under the curve 0.89, 95% confidence interval 0.81-0.98) whilst the standard error of the mean method indicated a value of 33 m. Similar values were obtained when only subjects with idiopathic pulmonary fibrosis were included (29 and 34 m, respectively). CONCLUSIONS: Small differences in six-minute walk distance, in the range 29-34 m, may be clinically significant for people with diffuse parenchymal lung disease.