The authors investigated what risk factors contribute to an excess risk of poor adult health among children who experience socioeconomic disadvantage. Data came from 1,037 children born in Dunedin, New Zealand, in 1972-1973, who were followed from birth to age 32 years (2004-2005). Childhood socioeconomic status (SES) was measured at multiple points between birth and age 15 years. Risk factors evaluated included a familial liability to poor health, childhood/adolescent health characteristics, low childhood intelligence quotient (IQ), exposure to childhood maltreatment, and adult SES. Adult health outcomes evaluated at age 32 years were major depressive disorder, anxiety disorders, tobacco dependence, alcohol or drug dependence, and clustering of cardiovascular disease risk factors. Results showed that low childhood SES was associated with an increased risk of substance dependence and poor physical health in adulthood (for tobacco dependence, sex-adjusted relative risk (RR) = 2.27, 95% confidence interval (CI): 1.41, 3.65; for alcohol or drug dependence, RR = 2.11, 95% CI: 1.16, 3.84; for cardiovascular risk factor status, RR = 2.55, 95% CI: 1.46, 4.46). Together, the risk factors studied here accounted for 55-67% of poor health outcomes among adults exposed to low SES as children. No single risk factor emerged as the prime explanation, suggesting that the processes mediating the link between childhood low SES and adult poor health are multifactorial.