OBJECTIVES: Depression is a common co-morbidity among people living with HIV.  Co-morbid depression often leads to poor self-management and non-adherence to antiretroviral therapy which may result in increased use of emergency and inpatient care.  We aimed to examine impacts of co-morbid depression on acute health care utilization over time among this high-need population in Ontario.    METHODS: A longitudinal HIV+ cohort study of Ontarians(N=3,545) was undertaken from 2008-2012 by linking the Ontario HIV Treatment Network(OHTN) Cohort Study and the administrative health databases.  Co-morbid depression defined based on either the Center for Epidemiologic Studies Depression Scale(Scores>=20) or the Kessler Psychological Distress Scale(Scores>=23) was assessed from the yearly interviews.   Patterns of emergency and inpatient care utilization were assessed during the 12 months following each interview. Urgent and non-urgent emergency room visits were defined using the five-level Canadian Triage and Acuity Scale(CTAS).  Generalized mixed effect regressions were used to examine associations between the acute care utilization and the co-morbid depression over time.    RESULTS: At baseline, 950(27%) were identified with co-morbid depression. The HIV+ patients with co-morbid depression were more likely to be age<50 years(OR:1.6;95%CI:1.4-1.9), female(OR:1.6;95%CI:1.3-1.9), have CD4 count<200cell/mm(OR:1.3;95%CI:1.1-1.7) and have used non-medical drugs in past 6 months(OR:1.8;95%CI:1.5-2.1). The prevalence of the use of urgent and non-urgent emergency room and inpatient care for those with co-morbid depression were 58vs.42%,44vs.31%,13vs.7% when compared to their non-depressed counterparts.  Over the five-year follow-up, those with co-morbid depression were more likely to use urgent (Adjusted OR (aOR):1.7;95%CI:1.2-2.5) and non-urgent (aOR:1.4;95%CI:1.03-2.0) emergency services and to be hospitalized (aOR: 1.6;95%CI:1.3-2.1) when compared to their non-depressed counterparts after controlling for socio-demographics, clinical markers, and behaviourial confounders.   CONCLUSIONS: Co-morbid depression experienced in persons living with HIV significantly increases the use of acute care services.  Incorporation of strategies in managing and detecting co-morbid depression would be important to deliver successful HIV care in Ontario.