Previous research has shown a strong connection between birth weight and future child outcomes. But this research has not asked how insults to child health after birth affect long-term outcomes, whether health at birth matters primarily because it predicts future health or through some other mechanism, or whether health insults matter more at some key ages than at others? We address these questions using a unique data set based on public health insurance records for 50,000 children born between 1979 and 1987 in the Canadian province of Manitoba. These children are followed until 2006, and their records are linked to provincial registries with outcomes data. We compare children with health conditions to their own siblings born an average of 3 years apart, and control for health at birth. We find that health problems, and especially mental health problems in early childhood are significant determinants of outcomes linked to adult socioeconomic status.