The authors examined the relation between time since onset of illicit drug injection (time at risk) and rates of hepatitis C virus (HCV) infection by using meta-regression. In 72 prevalence studies, median time since onset of injection was 7.24 years and median prevalence was 66.02%. The model showed statistically significant linear and quadratic effects of time at risk on HCV prevalence and significantly higher prevalence in developing and transitional countries and in earlier samples (1985-1995). In developed countries post-1995, mean fitted prevalence was 32.02% (95% confidence interval: 25.31, 39.58) at 1 year of injection and 53.01% (95% confidence interval: 40.69, 65.09) at 5 years. In developing/transitional countries post-1995, mean fitted HCV prevalence was 59.13% (95% confidence interval: 30.39, 82.74) at 1 year of injection. In 10 incidence studies, median time at risk was 5.29 years and median cumulative HCV incidence was 20.69%. Mean fitted cumulative incidence was 27.63% (95% confidence interval: 16.92, 41.70) at 1 year of drug injection. The authors concluded that time to HCV infection in developed countries has lengthened. More rapid onset of HCV infection in drug injectors in developing/transitional countries resembles an earlier era of the HCV epidemic in other regions.