The use of FEV1/FEV6 in place of the traditional FEV1/FVC to detect airways obstruction during spirometry testing performed by primary care providers would reduce time and patient effort. We hypothesized that the FEV1/FEV6, would predict the subsequent decline in FEV1 in adult cigarette smokers who enrolled in the multicenter Lung Health Study. Ten clinical centers in the U.S. and Canada recruited 5887 male and female smokers, aged 35-60 years, with borderline to mild airways obstruction by spirometry. Those who successfully stopped smoking during the 5-yr study (usually as the result of the smoking cessation intervention) were excluded from this analysis. In those continuing to smoke, the relative strength of spirometric predictors of the change in FEV1 during 5 years of follow-up (DFEV1) was determined using a linear regression model. The following covariates were significant independent predictors of DFEV1: the baseline degree of airways obstruction, age, gender, cigarettes per day, years of education, and bronchial hyperresponsiveness. The FEV1/FEV6 was nearly as strong an independent predictor as was the FEV1/FVC (a traditional index of airways obstruction). The degree of airways obstruction, as determined by the FEV1/FEV6 from spirometry, is an independent predictor of subsequent decline in lung function; and therefore, may be used to detect smokers at higher risk of developing COPD. © 2002 Elsevier Science Ltd.