The incidence of hepatitis C virus (HCV) infections among human immunodeficiency virus (HIV)-infected men who have sex with men has increased in recent years and is associated with high-risk sexual behavior. Behavioral interventions that target high-risk behavior associated with HCV transmission and treatment with direct-acting antivirals may prevent further HCV infections. We predicted the effect of behavioral and treatment interventions on HCV incidence and prevalence among HIV-infected men who have sex with men up to 2030 using a HCV transmission model parameterized with data from the Swiss HIV Cohort Study. We assessed behavioral interventions associated with further increase, stabilization, and decrease in the size of the population with high-risk behavior. Treatment interventions included increase in treatment uptake and use of direct-acting antivirals. If we assumed that without behavioral interventions high-risk behavior spread further according to the trends observed over the last decade and that the treatment practice did not change, HCV incidence converged to 10.7/100 person-years. All assessed behavioral interventions alone resulted in reduced HCV transmissions. Stabilization of high-risk behavior combined with increased treatment uptake and the use of direct-acting antivirals reduced incidence by 77% (from 2.2 in 2015 to 0.5/100 person-years) and prevalence by 81% (from 4.8% in 2015 to 0.9%) over the next 15 years. Increasing treatment uptake was more effective than increasing treatment efficacy to reduce HCV incidence and prevalence. A decrease in high-risk behavior led to a rapid decline in HCV incidence, independent of treatment interventions. CONCLUSION Treatment interventions to curb the HCV epidemic among HIV-infected men who have sex with men are effective if high-risk behavior does not increase as it has during the last decade; reducing high-risk behavior associated with HCV transmission would be the most effective intervention for controlling the HCV epidemic, even if this was not accompanied by an increase in treatment uptake or efficacy. (Hepatology 2016).