In a 16-year mortality followup of some 293,000 insured U.S. veterans, specific causes of death were studied in relation to smoking status. The main results confirmed earlier findings.Mortality ratios for cigarette smokers as compared with nonsmokers were 1.73 for all causes of death, 1.58 for all cardiovascular diseases, 2.12 for all cancers, and 4.31 for all respiratory diseases. The highest ratios (those greater than 5.0) were observed for cor pulmonale, aortic aneurysm, emphysema and bronchitis, cancer of the pharynx, cancer of the esophagus, cancer of the larynx, and cancer of the lung and bronchus. The greatest excess in deaths in terms of observed numbers minus expected was found for the cardiovascular diseases, in particular for coronary heart disease.Mortality ratios for ex-cigarette smokers who had stopped smoking for reasons other than physicians' orders were much lower compared with nonsmokers than the mortality ratios for current cigarette smokers: 1.21 for all causes, 1.15 for all cardiovascular diseases, 1.39 for all cancers, and 2.08 for all respiratory diseases. For most causes of death, the mortality ratios for ex-cigarette smokers who had stopped smoking for reasons other than physicians' orders varied inversely with the number of years of cessation. For some diseases, the mortality risk for the ex-cigarette smoker returned to normal almost immediately after the cessation of smoking, whereas for others, the return to normal was more gradual. The first group included stroke and the combined category of influenza and pneumonia; the second group included cardiovascular diseases as a whole and coronary heart disease. For still other diseases, although the mortality ratio declined with the length of time smoking was discontinued, substantial excess risks remained even after 20 years of cessation. In this third group were aortic aneurysm, bronchitis and emphysema, and lung cancer-diseases with very high mortality ratios for current cigarette smokers. Parkinson's disease remained the one disease that clearly exhibited a negative association with cigarette smoking.