During past 16 years, 192 patients underwent surgery for myasthenia gravis including 40 patients with pure ocular symptoms in our institute. In these 40 patients, 8 were associated with thymoma. The clinical stages of the thymomas were registered into Stage I (n = 5), Stage II (n = 1), Stage III (n = 1), Stage IV (n = 1) according to the classification of Masaoka and colleagues. All patients underwent extended thymothymectomy. The patient in stage III had been well until generalized myasthenic symptoms appeared 4 years after the surgery. Since the chest X-ray film revealed the tumor shadow on the right diaphragm, removal of the tumor was performed. Although he developed myasthenic crisis postoperatively, he is well controlled medically. Other 7 patients have been doing well. We concluded that a close postoperative follow up should be performed for the patients with ocular type myasthenia gravis associated with thymoma.