The purpose of this study was twofold: (1) To investigate the individual- and system-level characteristics associated with high utilization of acute mental health services according to a widely-used theory of service use-Andersen's Behavioral Model of Health Service Use -in individuals enrolled in a large, public-funded mental health system; and (2) To document service utilization by high use consumers prior to a transformation of the service delivery system. We analyzed data from 10,128 individuals receiving care in a large public mental health system from fiscal years 2000-2004. Subjects with information in the database for the index year (fiscal year 2000-2001) and all of the following 3 years were included in this study. Using logistic regression, we identified predisposing, enabling, and need characteristics associated with being categorized as a single-year high use consumer (HU: >3 acute care episodes in a single year) or multiple-year HU (>3 acute care episodes in more than 1 year). Thirteen percent of the sample met the criteria for being a single-year HU and an additional 8% met the definition for multiple-year HU. Although some predisposing factors were significantly associated with an increased likelihood of being classified as a HU (younger age and female gender) relative to non-HUs, the characteristics with the strongest associations with the HU definition, when controlling for all other factors, were enabling and need factors. Homelessness was associated with 115% increase in the odds of ever being classified as a HU compared to those living independently or with family and others. Having insurance was associated with increased odds of being classified as a HU by about 19% relative to non-HUs. Attending four or more outpatient visits was an enabling factor that decreased the chances of being defined as a HU. Need factors, such as having a diagnosis of schizophrenia, bipolar disorder or other psychotic disorder or having a substance use disorder increased the likelihood of being categorized as a HU. Characteristics with the strongest association with heavy use of a public mental health system were enabling and need factors. Therefore, optimal use of public mental services may be achieved by developing and implementing interventions that address the issues of homelessness, insurance coverage, and substance use. This may be best achieved by the integration of mental health, intensive case management, and supportive housing, as well as other social services.