The associations of social relationships, socioeconomic status and health practices with 20-year mortality were examined in a cohort of 2000 Ontario males. A social relationships index comprised of marital status, number of children, family contact and participation in voluntary associations had a strong association with mortality (adjusted relative risk of 0.30, 95% CI 0.11-0.83, comparing the highest 10% with the lowest 10% scores of the index). Among indicators of socioeconomic status, only income was significantly related to mortality with an adjusted relative risk of 0.41 (95% CI 0.23-0.72) for the highest 20% compared with the lowest 20% income group. The adjusted relative risk for smokers compared with non-smokers was 2.26 (95% CI 1.51-3.37). The joint effects of a relatively high score in the social relationships index, high income and being a non-smoker is estimated to represent an approximately 18-fold reduction in the risk of mortality during the follow-up period.