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.