This study focuses on the association between homeless veterans' prior utilization of medical, psychiatric, and substance abuse services and biopsychosocial characteristics reported at admission into a domiciliary care program. Given the large number of veterans in the US homeless population and their health care needs, understanding factors associated with health service use among homeless veterans is significant. Research participants were 429 homeless male veterans who had been admitted to the Domiciliary Care for Homeless Veterans Program site at the West Los Angeles Veterans Affairs Medical Center between February 1988 and July 1992 for treatment of medical, psychiatric, or substance disorders. Results of logistic regression analyses indicated that self-reported need (chronic medical problems, serious psychiatric symptoms, combat stress, alcohol use) and evaluated need for care (evidence of liver dysfunction) were important to veterans' use of health services in the 6 months before program admission. Predisposing social structure factors (education, residential stability, and usual sleeping place) were also significant predictors of service utilization. Overall, need factors were more strongly related to service use. Supplementary logistic regression analyses indicated that comorbidity of need factors deserves attention in understanding homeless veterans' use of services. In conclusion, it is important to attend to predisposing social structure factors as potential barriers to care for homeless veterans.