This study examines whether men who were born outside marriage in early twentieth century Sweden run a higher risk of dying from ischaemic heart disease (IHD) in middle and old age compared to men who were born inside marriage. Analyses are based on the male half of the Uppsala Birth Cohort Study, Sweden, consisting of all 7411 boys who were born alive at the Uppsala Academic Hospital during the period 1915-1929. The statistical method used is Cox regression. The results demonstrated a statistically significant excess mortality among men born outside marriage, which could not be explained by either social class of origin or birth weight for gestational age. Instead, this elevated mortality was largely explained by the more than doubled mortality risk among those men born outside wedlock who never married in relation to the corresponding group of men born to married parents. Even when three indicators of adult socio-economic status were adjusted for, men who never married and were born outside marriage still ran a 93 per cent higher risk of dying from IHD than men who never married but were born inside marriage. This intervening effect of adult marital status was restricted to the category of never married men. Thus, although divorcees demonstrated an even higher mortality risk in relation to the married than did those who never married, this was equally true for men born inside and men born outside marriage. In the concluding section of the paper I argue that these findings should be understood in terms of the childhood social stigma that the illegitimate children experienced. This stigma may have resulted in an increased susceptibility, which in combination with the "failure" in adulthood to comply with the established norms of society regarding matrimony led to higher levels of IHD mortality in middle and old age.