BACKGROUND: Persons with mental disorders frequently have other co-occurring problems such as substance related disorders and HIV/AIDS. Individuals with co-occurring medical and mental disorders encounter great obstacles to receiving mental health services. AIMS: This paper uses the Behavioral Model of Vulnerable Populations to evaluate use of mental health services among groups with co-occurring disorders (CODs) and other co-morbid relationships. The association between receipt of mental health treatment and traditional/vulnerable predisposing, enabling, and need factors are examined. METHODS: Bivariate analysis and two-stage hierarchical logistic regression were completed. RESUTLS: A sample of 553 persons who reported mental health problems within the past year had one or more of the following vulnerabilities: (1) substance disorders; (2) homelessness; (3) victims of violent crime; (4) diagnosed with HIV/AIDS; (5) recipient of public benefits; and 31.3% reported having received some form of mental health treatment. Both traditional and vulnerable characteristics are significant predictors of receipt of mental health treatment. Vulnerable predictors indicated decreased odds of receiving mental health treatment were associated with injection and chronic drug use, (OR = .42, CI: .22 - .77) and (OR = .38, CI: .22 - .64) respectively. CONCLUSION: The Behavioral Model of Vulnerable Populations could be employed in future research of CODs and other co-morbid group's utilization of mental health treatment.