STUDY OBJECTIVE: To examine the role of specialist outreach in supporting primary health care and overcoming the barriers to health care faced by the indigenous population in remote areas of Australia, and to examine issues affecting its sustainability. DESIGN: A process evaluation of a specialist outreach service, using health service utilisation data and interviews with health professionals and patients. SETTING: The Top End of Australia's Northern Territory, where Darwin is the capital city and the major base for hospital and specialist services. In the rural and remote areas outside Darwin there are many small, predominantly indigenous communities, which are greatly disadvantaged by a severe burden of disease and limited access to medical care. PARTICIPANTS: Seventeen remote health practitioners, five specialists undertaking outreach, five regional health administrators, and three patients from remote communities. MAIN RESULTS: The barriers faced by many remote indigenous people in accessing specialist and hospital care are substantial. Outreach delivery of specialist services has overcome some of the barriers relating to distance, communication, and cultural inappropriateness of services and has enabled an over fourfold increase in the number of consultations with people from remote communities. Key issues affecting sustainability include: an adequate specialist base; an unmet demand from primary care; integration with, accountability to and capacity building for a multidisciplinary framework centred in primary care; good communication; visits that are regular and predictable; funding and coordination that recognises responsibilities to both hospitals and the primary care sector; and regular evaluation. CONCLUSIONS: In a setting where there is a disadvantaged population with inadequate access to medical care, specialist outreach from a regional centre can provide a more equitable means of service delivery than hospital based services alone. A sustainable outreach service that is organised appropriately, responsive to local community needs, and has an adequate regional specialist base can effectively integrate with and support primary health care processes. Poorly planned and conducted outreach, however, can draw resources away and detract from primary health care.