BACKGROUND: Interferon α (IFN-alpha) is widely used in the treatment of viral infections, including hepatitis C. Unfortunately depression is a common side effect of IFN-alpha therapy. The presence of depressive symptoms is important because they have an adverse effect on the course of the illness and reduce the quality of life and the treatment adherence. The current prospective study examines the effects of IFN-alpha on the development of depressive disorders, on cognitive functioning and on quality of life. METHOD: A total of 25 patients with chronic hepatitis C infection were investigated. All patients were treated in the Department of Gastroenterology and Hepatology, University of Medicine of Graz, Austria. Psychometric observer rating and self-rating scales were administered 1 month and 3 months after the beginning of the antiviral treatment to evaluate depressive symptoms [Beck Depression Inventory (BDI); Hamilton Depression Scale]. The data on life satisfaction before therapy and health-related quality of life were obtained from the Fragebogen zur Lebenszufriedenheit (FLZ) and the SF-36 (Health Status Questionnaire). Cognitive function was based on the SKT (Syndrom Kurztest). All patients completed the Social Support Questionnaire (SSS), a multidimensional self-report measure of social support. RESULTS: Three months after the initial IFN-alpha administration in the whole sample significant impairments in health-related quality of life were found in the health-related domains "physical functioning", "role physical", "role emotional", "social functioning" and "vitality". The whole sample showed cognitive impairments. No changes in social support were recorded. Three months after the first INF-alpha administration, 48% (n=12) of the sample suffered from moderate clinical depression. In comparison to patients without pathological affective findings, patients with INF-alpha-induced clinical depression showed decreased life satisfaction before the initial antiviral therapy. Impairments in health-related quality of life (SF-36) were found in the sample with clinical depression in the health-related domains "general health", "social functioning", "role emotional", "vitality" and "mental health". CONCLUSION: Hepatitis C is associated with an increased prevalence of psychiatric disorders, particularly depression. INF-alpha patients having low levels of life satisfaction in the domains "self-concept" (skills, appearance, self-confidence, vitality …), "employment" and "physical health and constitution" seem to face a major risk of depression.