Differences between men and women regarding morbidity have been investigated in relation to tobacco smoking, among 2,009 70-year-olds in the longitudinal gerontological study in Gothenburg, Sweden. Male smokers (44%) had started smoking earlier (age 18) than female (14%, age 30), consumed more tobacco and more often inhaled tobacco smoke. Peptic ulcer, chronic bronchitis and lung cancer were examples of diseases more common in males. ECG evidences of myocardial ischemia were more common in males, while anginal pain showed the same prevalence. Cholecystectomy and antihypertensive treatment were more common among females. When adjustments were made for duration of smoking, amount of tobacco consumed, significant sex differences were still observed for ECG evidence of myocardial ischemia (dominance in males), peptic ulcer (dominance in males), intermittent claudication (dominance in females) and treatment for hypertension (dominance in females). The majority of disorders predominant in males were found to be related to smoking, while those predominating among females showed the same sex difference when adjustments were made for smoking habits. Future increasing segments of females addicted to tobacco smoking will obviously markedly influence sex difference in morbidity.