Aim The aim of this study is to examine the age-appropriate immunisation coverage and the factors associated with this in a cohort of Aboriginal infants in an outer urban Sydney community in comparison with non-Aboriginal infants in this community. Methods Data on immunisation coverage were extracted from the Australian Childhood Immunisation Register for a birth cohort of 178 Aboriginal and 356 non-Aboriginal infants born in Campbelltown between October 2005 and May 2007. Non-Aboriginal infants were matched on birthdates and gender. Data on maternal socio-economic and other characteristics were collected by questionnaire. Results Australian Childhood Immunisation Register records were identified for 92% of infants. Immunisation rates of Aboriginal infants were comparable with those of non-Aboriginal infants except for delay at 4 and 6 months. Rates of delay in immunisation at 12 and 18 months for both Aboriginal and non-Aboriginal infants were similar. Young maternal age and higher parity were both associated with a greater likelihood of delay. Conclusions Immunisation rates in this population of Aboriginal infants are comparable to those of non-Aboriginal infants except for delay in immunisation at 4 and 6 months. Identified risk factors for both Aboriginal and non-Aboriginal infants may be amenable to intervention. Strategies to ensure timely compliance with immunisation schedules in this outer urban community have achieved reasonable immunisation coverage for Aboriginal and non-Aboriginal infants.