The aim of the study was to examine the effects of parental socioeconomic status, own socioeconomic status and social mobility upon the development of smoking from adolescence to adulthood. Subjects were the participants of the North Karelia Youth Project study from six schools in Eastern Finland. At the baseline in 1978 they were 13 year-olds (n=903) and in the last of the six surveys in 1993 they were 28-year-olds. The parents were studied in 1978 and 1980. The association between smoking and socioeconomic status was measured by education, occupation and income in adolescence and adulthood, and social mobility was measured by the difference between parental and own education. In general, parental socioeconomic status was not significantly associated with the subjects' smoking in adolescence or adulthood. Own socioeconomic status measured at the age of 21 and 28 was strongly related to smoking. Those who were most educated in adulthood had smoked the least already from the age of 13. Social mobility was not significantly associated with smoking. The study stresses the importance of own socioeconomic status in relation to smoking, but parental socioeconomic status or social mobility does not have direct effects on smoking. Socioeconomic differences in smoking should be understood as an important determinant for health inequalities.