BACKGROUND: The additional burden of HCV infection in HIV-HCV coinfected individuals may have some consequences on adherence to highly active antiretroviral therapy (HAART). Few studies have explored the pattern of correlates of non-adherence to HAART while simultaneously considering the impact of HCV treatment and depressive symptoms on adherence to HAART. We used longitudinal data to assess factors associated with non-adherence to HAART. METHODS: The French national prospective cohort ANRS-CO-13-HEPAVIH is a multi-center cohort which recruited 1175 HIV-HCV coinfected patients in 17 hospital outpatient units delivering HIV and HCV care in France between October 2006 and June 2008. For this analysis, we selected participants on HAART with self-reported data for adherence to HAART (n = 727 patients, 1190 visits). Data were collected using self-administered questionnaires and medical records. A mixed logistic regression model based on an exchangeable correlation matrix was used to identify factors associated with non-adherence to HAART. RESULTS: Patients reported non-adherence to HAART in 808 (68%) of the 1190 visits. Four variables remained associated with non-adherence to HAART after multivariate analysis: hazardous alcohol consumption, cocaine use and depressive symptoms, regardless of whether treatment for depression was being received. Finally, patients being treated for HCV infection were less likely to be non-adherent to HAART. CONCLUSIONS: Besides the problem of polydrug use, two other dimensions deserve special attention when considering adherence to HAART in HIV-HCV coinfected patients. Access to HCV treatment should be encouraged as well adequate treatment for depression in this population to improve adherence and response to HAART.