A case of Basedow's disease, that developed after successful treatment of ulcerative colitis with a total colectomy, is presented, along with a review of the Japanese literature on the coexistence of hyperthyroidism and ulcerative colitis. A 26-year-old man was referred to our department, complaining of general fatigue, appetite loss, and palpitation. At age 14, blood was discovered in his stool and a diagnosis of ulcerative colitis was made. Since then, he has been treated with salazosulfapyridine and prednisolone. On examination, mild exophthalmos and thyroid swelling were observed. Both serum free T3 and T4 levels were increased along with a positive TSH receptor antibody, while TSH was decreased. Scintigraphic and ultrasonographic examinations of the thyroid gland showed diffuse enlargement. Treatment with thiamazole relieved the symptoms and normalized the thyroid function. Although a high incidence of autoimmune thyroid diseases in association with ulcerative colitis has been suggested, only 6 cases of hyperthyroidism coexisting with ulcerative colitis have been reported in Japan. A common immunological process has been suggested to be implicated in the pathogenesis of this association, however, the exact mechanism remains unclear.