Circumstances over the life-course may contribute to adult social class differences in mortality. However, it is only rarely that the life-course approach has been applied to mortality studies among young adults. The aim of this study is to determine to what extent social class differences in mortality among young Finnish men are explained by living conditions in the parental home and life paths related to transitions in youth. The data for males born in 1956-60 based on the 1990 census records are linked with death records (3184 deaths) by cause of death for 1991-98, and with information on life-course circumstances from the 1970, 1975, 1980, and 1985 censuses. Controlling for living conditions in the parental home-social class, family type, number of siblings, language and region of residence-reduced the high excess mortality of the lower non-manual (RR 1.51, 95% CI: 1.28-1.79), skilled manual (RR 2.94, 2.54-3.40), and unskilled manual class (RR 4.08, 3.51-4.73) by 10% in all-cause mortality. The equivalent reduction for cardiovascular disease was 28% and for alcohol-related causes 16%. The effect of parental home on mortality differences was mainly mediated through its effect on youth paths (pathway model). Educational, marital, and employment paths had a substantial effect-independent of parental home-on social class differences from various causes of death. When all these variables were controlled for adult social class differences in cause specific mortality were reduced by 75-86%. Most of this reduction in mortality differences can be attributed to educational path. However, marital and employment paths had their independent effects, particularly on the excess mortality of unskilled manual workers with disproportionately common exposure to long-term unemployment and living without a partner. In summary, social class differences in total mortality among men in their middle adulthood were only partly determined by parental home but they were mainly attributable to educational, marital, and employment paths in youth.