Psychosocial factors influencing smoking cessation were studied in current smokers prior to quitting. Two questionnaires were sent in 1975 and 1981 to adult members of the Finnish Twin Cohort. The 1975 response rate was 89%, and 89% of those eligible replied again in 1981. Analysis was done on data from one twin pair member only. Three groups were identified: 3617 never smokers, 2654 persistent smokers, and 823 quitters (i.e. current smokers in 1975, former smokers in 1981). Univariate and multivariate comparisons of baseline psychosocial variables for quitters and persistent smokers were performed in men aged 20-34 and 35-54 and women aged 20-39. Among women and young men quitters were better educated and scored lower on neuroticism. Young male quitters also slept longer, had been less often unemployed and drank less alcohol and coffee. Among middle-aged men quitters were more often married, slept longer, and had higher life satisfaction. The possibility that the influence of psychosocial factors on chronic disease may be mediated in part through changes in smoking behavior is discussed.