Predictors of obstructive airways disease (OAD) have been identified, and models for estimating risk of developing OAD have been derived for the adult population of Tecumseh. Men and women 16 to 64 yr of age when first studied were reexamined after an average interval of 15 yr. Incidence rates of OAD increased with age and were higher in men than in women more than 45 yr of age. Incidence rates were significantly higher in men and women with low degrees of lung function initially, and in cigarette smokers, especially those who continued to smoke. Other risk factors included a physician's diagnosis of chronic bronchitis, or asthma, a history of cough, wheeze, shortness of breath, frequent upper or lower respiratory tract infections, bronchitis or pneumonia, leanness, and familial chronic bronchitis. Multiple logistic regression analyses identified combinations of risk factors that placed 70% of the male and 73% of the female incidence cases in the top 10% of the risk distribution. The excess risk of obstructive airways disease associated with cigarette smoking and reduced lung function and the benefits of stopping smoking are clearly apparent. For example, the risk of developing obstructive airways disease in the next 15 years is about 1 in 200 for a 45-yr-old male nonsmoker whose Vmax50 equals to 100% of predicted, if he doesn't take up smoking. The risk for a man of the same age who smokes 40 cigarettes a day and whose Vmax50 equals 80% of predicted is 1 in 5 or 6 if he doesn't cut down on his smoking and about 1 in 15 if he stops smoking.