To ascertain the impact of hepatitis C virus (HCV) infection on human immunodeficiency virus (HIV) disease progression and associated death in the era of highly active antiretroviral therapy (HAART), we examined mortality rates, the presence of other diseases, and antiretroviral use in an observational cohort of 823 HIV-infected patients with and without HCV coinfection during the period of January 1996 through June 2001. Analyses were used to compare patient characteristics, comorbid conditions, and survival durations in HIV-infected and HIV-HCV-coinfected patients. HIV-HCV-coinfected persons did not have a statistically greater rate of acquired immunodeficiency syndrome or of renal or cardiovascular disease, but they did have more cases of cirrhosis and transaminase elevations. There were proportionately more deaths in the HIV-HCV-coinfected group. Age, baseline CD4+ cell count, and duration of HAART were significantly associated with survival, but HCV infection was not. HAART use was a strong predictor of increased duration of survival, suggesting that treatment is more important to survival than is HCV coinfection status.