Combined pegylated interferon and ribavirin therapy for chronic hepatitis C infection cause a wide range of side effects, including flu-like syndrome, hematological abnormalities, cardiovascular symptoms, gastrointestinal symptoms, pulmonary dysfunction, depression, and retinopathy. Interferon-alpha has been shown to be related to the development of various autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis, autoimmune thyroid disease, and type 1 diabetes mellitus (DM). Type 1 DM and thyroid disease respectively develop in 0.08-2.61% and 10-15% of patients treated with combined interferon-alpha and ribavirin for chronic hepatitis C. The coexistence of type 1 DM and autoimmune thyroiditis was rarely reported. We report a case of a 33-year-old female patient with chronic hepatitis C who simultaneously developed diabetic ketoacidosis and autoimmune thyroiditis after treatment with pegylated interferon-alpha 2b and ribavirin.