We assessed the relation of cigarette smoking to mortality in an 11-year follow-up study of 4004 men and women, 35 to 54 years of age, who responded to urging to have multiphasic health checkups. Accounting for 48 other characteristics, both individually and in combination, failed to eliminate the association of smoking with mortality from all causes or with mortality from coronary heart disease. The smoker-to-nonsmoker mortality ratios, crude and adjusted respectively, were 2.6 and 2.1 for all causes and 4.7 and 3.6 for coronary heart disease. This analysis did not support the counterhypothesis that the association of cigarette smoking with mortality is secondary to some underlying characteristic.