With marital breakdown and discord relatively common, we examined whether family structure and the quality of marital relationship have a long-term impact on offspring’s psychopathology in early adulthood. This study aimed to examine the association of family structure and marital discord in the family with a wide range of offspring’s mental health and problem behaviours at 21 years. Data were from the Mater-University of Queensland Study of Pregnancy, a population based birth cohort study, which commenced in Brisbane, Australia in 1981. Mothers and children were followed up at birth, 6 months and 5, 14 and 21 years after the initial interview. Marital status and marital quality were assessed at the 14 year follow-up. Young Adult Self-Report sub-scales of mental health and problem behaviours were measured at the 21-year follow-up. Type of family structure and the quality of marital relationship (at the 14-year follow-up) predicted offspring’s psychopathology at 21 years. When a selected group of confounding factors were included in the multivariate analyses, children who lived with a step-father, un-partnered mother, or in families where parents had conflict in marital relationship reported higher symptoms of psychopathology at 21 years. The association between marital problems and young adult psychopathology does not appear to be confounded by a wide range of confounding variables. Further research is needed to explore the mechanism of these associations to develop preventive programmes.