We encountered a rare operative case of hyperthyroidism followed by ulcerative colitis (UC). A 26-year-old mam was referred to our department to undergo an operation. We suspected the possible complication of adrenal insufficiency, since he suffered from severe weight loss, a high fever and palpitation on admission. We diagnosed hyperthyroidism, however, based on the presence of high serum free T3 and T4 levels and a decreased TSH level. After improving the symptoms and the thyroid function by administering thiamazole, we then performed a total proctocolectomy. Although a high rate of association of autoimmune thyroid diseases with UC has been suggested, only 9 cases of hyperthyroidism coexisting with UC have so far been reported in Japan. A common immunological process has been suggested to be implicated in the pathogenesis of this association, however, the exact mechanism needs to be elucidated in the future.