Analyzing six minute walk distances from 822 people with idiopathic pulmonary fibrosis in an interferon-gamma-1b clinical trial, du Bois et al found those whose decline in six minute walk test distance was >50 meters in 24 weeks had a four-fold risk of death within one year. In everyone but those with the very worst functional status, 6MWT distance did not correlate well with physiologic measures. The authors propose adding 6MWT decline as an outcome measure to clinical trials for IPF, which should reduce trials' required size. They propose a minimally clinically important difference for 6MWT of 24 to 45 m. AJRCCM 2011;183:1231-1237.