Introduction/Aim: Chronic viral hepatitis and its treatment with interferon (IFN) have an impact on patients' quality of life. The purpose of this study was to evaluate the degree of depression in patients with chronic viral hepatitis before and during IFN therapy. Patients/Methods: Our study group comprised 132 patients, 38 with chronic hepatitis C (26 males, 12 females), 36 with chronic hepatitis B (29 males, 7 females), and 58 individuals with no chronic disease (24 males, 34 females). Depression was assessed using the Zung Self-Rating Depression Scale and the corresponding SDS index. Results: At baseline, patients with viral hepatitis and healthy controls had similar SDS indexes. During treatment, a significant increase in the SDS index was observed in both HBV and HCV patients (p < 0.001), which returned to the baseline levels after treatment. During IFN therapy, the SDS indexes were higher in HCV compared to HBV patients and women compared to men (p = 0.001 and p = 0.008, respectively), and there was a >5- fold increased frequency to develop severe depression. Conclusions: IFN-induced depression occurs more frequently in HCV than HBV patients and in women than men. Monitoring during treatment is mandatory in order to maximize treatment adherence. Copyright (C) 2002 S. Karger AG, Basel.