ObjectivesZZThe aim of this study was to clarify anxiety symptoms associated with the pegylated interferon (PEG-IFN) treatment and to determine which factors are associated with these anxiety symptoms. MethodsZZThe subjects were 30 patients with hepatitis B and C viral infections who were waiting to receive PEG-IFN treatment. For assessment of depressive and anxiety symptoms, the Beck Depression Inventory and the State-Trait Anxiety Inventory were used. Patients were examined before treatment and then prospectively during the 2 weeks, 4 weeks and 1 years of therapy. We analyzed the changes in anxiety and depression symptoms, and applied multiple regression analysis to identify factors that significantly affect the anxiety symptoms. ResultsZZCompared to pre-treatment baseline, anxiety symptoms increased 2 weeks after treatment, and gradually decreased 4 weeks, and 1 year after treatment. And, we analyzed the sub-factors of depressive symptoms that affect the anxiety symptoms. After 2 weeks of treatment, cognitive-affective factors and hypochondriasis factors of depressive symptoms had an effect on anxiety symptoms. Furthermore after 4 weeks of treatment, the cognitive-affective factors had an effect on anxiety symptoms. ConclusionZZIn this study, we found a significant increase in anxiety symptoms after PEG-IFN treatment, and cognitive-affective depressive factors significantly affect anxiety symptoms.