Encouraged by recent results with "extended" thymectomy in the treatment of myasthenia gravis, we carried out repeat thymectomy in six patients with chronic, refractory disease who did not initially have extended thymectomy. All were completely disabled with longstanding myasthenia. Initial thymectomy (four transsternal, one transcervical, and one substernal) was carried out at a mean of 8.9 years previously (range, 5 to 18). There was no residual thymus observed with CT, but at repeat thymectomy, residual thymic tissue was present in five of six patients. Five patients significantly improved and four returned to full-time work. Mean prednisone dose declined from 51 mg to 18 mg/d, and mean pyridostigmine dose fell from 1,290 mg to 415 mg/d. No patient to date has had a complete remission. These results suggest that repeat thymectomy may benefit some patients with chronic disabling myasthenia gravis, especially when it is uncertain from a review of the operative report whether all thymic tissue was removed at the initial thymectomy.