Background:Hepatitis C is a major cause of liver-related morbidity and mortality and represents a major public health problem in Egypt and worldwide. INF therapy is the most popular treatment for HCV. INF has many side effects most of them still under study. The development of thyroid dysfunction during IFN and Ribavirin combination therapy has been reported.   Aim:The aim of this study is to assess the Prevalence of thyroid dysfunction in Egyptian chronic hepatitis C patient treated with pegylated interferon and Ribavirin   Materials & Methods:The study was conducted in cooperation between Internal Medicine Department, Faculty of Medicine, Cairo University and Internal Medicine Department, out patients' clinic of National Hepatology and Tropical Medicine Research Institute (NHTMRI) in the period from January 2009 to June 2010. The current study included 200 patients who fulfilled the predesigned inclusion criteria. TSH was done pre treatment, every 3 months during treatment and 3 months following termination of treatment also were done for all cases. Also, FT3 and FT4 were done if there is abnormal TSH.   Results: The prevalence of thyroid dysfunction in chronic hepatitis C patients treated with pegylated INF and Ribavirin reaching 19% in this study.