OBJECTIVE: The purpose of the study was to develop a descriptive profile of heavy users of services in the South Australian Mental Health Services. METHODS: Case notes for 50 heavy users were reviewed to obtain demographic and diagnostic information and data on service use over a three-year period. To supplement and verify this information, 35 of the patients were given structured interviews. RESULTS: The mean age of the 50 patients was 34.9 years, and there was a slight predominance of females. Most patients had never married and had been unemployed for a long time. All had a low income. The mean number of years of education was ten. The group was seriously disabled by psychiatric illness. The most common diagnosis was schizophrenia, followed by schizoaffective disorder and bipolar disorder. Comorbid axis I disorder and personality disorder or physical illness was common. Drug and alcohol abuse often complicated patient management and patients' ability to live successfully in the community. The average annual cost per patient was $13,598 (Australian), largely from inpatient care. CONCLUSIONS: This study contributes to an emerging global profile of the heavy service user. Such a profile may help service systems identify patients in this subgroup and target management strategies to these often very disadvantaged and challenging patients.