Neutropenia during treatment with peginterferon alfa and ribavirin for chronic hepatitis C virus (HCV) infection is a common cause of dose reductions of peginterferon alfa. These reductions are performed to prevent bacterial and fungal infections, which are common during HCV treatment and can be attributed to neutropenia. The aims of this study were to investigate the occurrence of infections and their relation to neutropenia and to identify potential risk factors for infections during HCV treatment. In this single-center cohort study, 2,876 visits of 321 patients treated with peginterferon alfa and ribavirin were evaluated for neutropenia, infections, dose reductions, and potential risk factors for infection during HCV treatment. The baseline mean absolute neutrophil count (ANC) was 3,420 cells/?L, and 16 patients had a baseline ANC of <1,500 cells/?L. During treatment, neutropenia, which was defined as ANC <750 cells/?L, was observed in 95 patients (29.7%) and ANC <375/?L was observed in 16 patients (5%). Ninety-six infections were observed in 70 patients (21.8%). Thirteen infections (13.5%) were defined as severe. Infections were not correlated with neutropenia during treatment. Dose reductions did not lead to a decrease in infection rate. Multivariate logistic regression analysis revealed that age >55 years (odds ratio [OR] 2.06, 95% confidence interval [CI] 1.19-3.56, P = 0.01) and baseline hyperglycemia (OR 2.17, 95% CI 1.15-4.10, P = 0.016) were associated with an increased risk of infection during HCV treatment. Cirrhosis and chronic obstructive pulmonary disease were not risk factors for infection. Conclusion: Bacterial infections during treatment with peginterferon alfa and ribavirin are not associated with neutropenia. Older patients and patients with poorly controlled diabetes mellitus have a greater risk of developing infections during HCV treatment.