Predictive factors for initiation of antiviral therapy in chronically infected hepatitis C virus (HCV) patients are not fully elucidated. The aim of this study was to determine predictive factors for initiation of treatment with standard or pegylated interferon either alone or combined with ribavirin. A Danish cohort of individuals chronically infected with HCV was used and observation time was calculated from the date of inclusion in the cohort to date of death, last clinical observation, 1 January 2007, or start of HCV antiviral treatment in treatment-naïve patients. Kaplan-Meier survival analysis was used to construct time to event curves. Cox regression was used to determine the incidence rate ratios as estimates of relative risk (RR) and 95% confidence intervals (CI). A total of 1780 patients were enrolled in the study. The cumulative chance of treatment initiation over 5 years was 33.0%. We found several strong predictors of treatment initiation: elevated alanine aminotransferase [>2 times upper limit (RR = 2.17, 95% CI 1.64-2.87), >3 times upper limit (RR = 3.64, 95% CI 2.75-4.81)], genotype 2 or 3 (RR = 1.86, 95% CI 1.49-2.31) and HIV co-infection (RR = 0.28, 95% CI 0.15-0.53). To our knowledge, this study is the first to estimate factors predicting initiation of antiviral treatment in patients with chronic HCV infection on a nationwide scale. We found that several of the factors predicting initiation of antiviral treatment correlate with factors known to predict a better response to treatment and factors known to increase the progression of liver disease.