The effect when persons quit smoking was studied in a prospective study of 855 50-year old men randomly selected from the general population of Gothenburg, Sweden. These men have been followed since 1963. For this report, data from the first ten years of follow-up were used. The survivors from this period were divided into three groups: those who had never smoked, those who were smokers at the first examination but not since (ex-smokers), and those who were smokers at all three examinations. Compared to ex-smokers, the smokers had a steeper decrease of bronchial peak flow, more days of sick leave, more complaints and poorer self-assessed life situation score. After adjusting for possible confounding factors and differences in morbidity prevalence between the groups at the start of the study, the smokers still had a more unfavorable health course than the ex-smokers.