Thymectomy has been shown to be effective in the treatment of myasthenia gravis. The logical goal of operation has been complete removal of the thymus, but there has been controversy about the surgical technique and its relation to results. Surgical-anatomic studies have shown gross and microscopic thymus widely distributed in the neck and mediastinum. We believe that an en bloc transcervical-transsternal "maximal" thymectomy is required to remove all thymic tissue predictably. Ninety-five patients with generalized myasthenia gravis underwent "maximal" thymectomy consecutively between 1977 and 1985 and were evaluated 6 months to 89 months after operation. In Group A (N = 72), myasthenia gravis without thymoma, the uncorrected data revealed that 96% (69) had benefited from operation: 79% (57) had no symptoms; 46% (33) were in remission; 33% (24) were symptom free when receiving minimal doses of pyridostigmine; and none were worse. Life table analysis yielded a remission rate of 81% at 89 months. In group B (N = 8), myasthenia gravis without thymoma for which patients underwent reexploration for incapacitating weakness after earlier transcervical or transsternal operations, residual thymus was found in all. One patient was in remission, two were symptom free when receiving medication, one was unchanged, and none were worse. In group C (N 15), myasthenia gravis and thymoma, two patients were in remission and nine were symptom free when receiving medication. Two patients in this group died 2 and 4 years postoperatively in crisis. Response to thymectomy in group A was greater in patients with mild myasthenia gravis and may have been better in patients who had symptoms for less than 60 months preoperatively, but the response did not depend on age, sex, presence or absence of thymic hyperplasia or involution, or titers of acetylcholine receptor antibodies. The response to thymectomy in group B was striking but slower than in group A, perhaps because symptoms were more severe and of longer duration. The response in group C was also less good than in group A and proportionately fewer benefited. These results support the recommendation for thymectomy in the treatment of patients with generalized myasthenia gravis and indicate the desirability of a maximal procedure. For persistent or recurrent severe symptoms after previous transcervical or submaximal transsternal resections, reoperation by this technique is also recommended.