Purpose: Our purpose in the current study was to examine the relationship between health services utilization delivered by means of the Homeless Outreach Medical Services (HOMES) program and health services utilization delivered by means of the Parkland emergency room and inpatient units among a sample of older and younger homeless adults being served by the Parkland Health and Hospital System. Design and Methods: The HOMES program uses two 40-ft-long mobile medical units and a fixed-site outpatient clinic to provide primary health care on a walk-in, no-charge basis to individuals who are homeless. We used a quasi-experimental design, and we randomly selected health services utilization data from 293 male (50.4%) and 288 female (49.6%) homeless patients from among the 14,876 homeless patients aged 20-64 years who used HOMES and the Parkland Health and Hospital System between June 1, 1992, and June 30, 1999. The dependent, variables were measurements of inpatient and outpatient utilization of psychiatric, substance abuse, and musculoskeletal services by homeless patients. Inpatient and outpatient utilization patterns by age were assessed. Data were analyzed using a split-plot repeated measures multivariate analysis of variance (MANOVA), one-way analysis of variance (ANOVA), and simple linear regression. Results: Older homeless individuals utilized the HOMES more than inpatient, services for substance abuse and musculoskeletal conditions, but they utilized inpatient services the most for psychiatric-related conditions. Implications: This level of inpatient utilization is perhaps a result, of greater severity or progression of mental illness among older homeless adults. The level of outpatient, utilization is probably because the HOMES program mitigates many of the barriers that, prevent homeless individuals from obtaining primary medical care.Key Words: Homeless person, Health service, Indigenous health services