Health care utilization for HIV-1-infected patients appears to be declining in the United States as a result of highly active antiviral therapy (HAART); yet the opposite appears true in the HIV/hepatitis C virus (HCV) coinfected population. The reasons for this difference are not well understood. We examined the rates and reasons for emergency department visits and hospital admissions at an academic tertiary care medical center for HIV/HCV coinfected patients as compared to HIV-1 monoinfected patients, using a retrospective matched cohort study design. HIV/HCV coinfected patients had higher rates of health care utilization (emergency department visits 43.9 versus 7.1 per 100 person-years; hospital admissions 18.2 versus 6.7 per 100 person-years, for HIV coinfected and monoinfected, respectively). This increase was not solely due to liver related events. Instead, comorbidities such as diabetes, renal disease, and psychiatric/substance abuse played a larger role in the health-care utilization in the HIV/HCV coinfected population.