A fifty-year-old woman was admitted to our hospital because of palpitation and general fatigue. She had received hemithyroidectomy for thyroid papillary adenocarcinoma at 28 years of age. She had experienced episodes of repeated painless thyroiditis five times over the last 12 years. At her sixth episode of thyrotoxicosis, she was suspected to have Graves' disease and admitted to our hospital. Laboratory findings revealed thyrotoxicosis with positive thyroid stimulating antibody and high radioactive iodine uptake, i.e. Graves' disease. Painless thyroiditis often relapses but rarely develops into Graves' disease. This is a rare case in which repeated painless thyroiditis was followed by Graves' disease. The relation between painless thyroiditis and Graves' disease is discussed.