This paper aims to describe delivery and birth outcomes of Aboriginal infants and their mothers in an urban setting on the east coast of Australia. The paper uses a causal pathway approach to consider the role of risk and protective factors for low birthweight. All mothers who delivered at Campbelltown Hospital between October 2005 and May 2007 were eligible. The study included 1,869 non-Aboriginal infants and 178 Aboriginal infants and their mothers. Information on delivery and birthweight was extracted from electronic medical records. Risk factors for poor outcomes were explored using regression and causal pathway analysis. Mothers of Aboriginal infants were younger than mothers of non-Aboriginal infants, and were more likely to be single, less educated, unemployed prior to pregnancy, and live in a disadvantaged neighbourhood. Health and service use was similar. They were significantly more likely to have a vaginal delivery than mothers of non-Aboriginal infants (77% cf 62.5%; χ (1) (2) = 14.6, P < 0.001) and less likely to receive intervention during delivery. Aboriginal infants (3,281.1 g) weighed 137.5 g (95%CI: 54-221 g; P = 0.001) less then non-Aboriginal infants (3,418.7 g). Gestational age, and single mother with incomplete education, prior unemployment, smoking, and living in a disadvantaged neighbourhood were associated with lower birthweight. Maternal vulnerability had a cumulative impact on birthweight. A causal pathway analysis demonstrated the associations between risk factors.