Purpose: Thymectomy has been widely employed in the treatment of myasthenia gravis (MG). However, little data exist in Iran demonstrating the efficacy and morbidity of thymectomy. The aim of this study was to determine the clinical features, diagnostic approach, and therapeutic outcome in patients with MG who underwent thymectomy. Methods: This historical cohort study was conducted in 3 university hospitals in Tehran. Preoperative and operative indices of 61 patients with MG who had been treated with thymectomy in these hospitals from September 2000 to July 2005 were reviewed. Among them, 20 patients were followed during one year after operation for determination of postoperative complications and one year mortality rate. Results: The most common manifestations of MG were ptosis (77.0%) and upper limbs weakness (70.4%). CT scans of the thymus showed thymus enlargement, thymoma and thymus hyperplasia in 51.5% (22/43), 11.6% (5/43) and 2.32% (1/43) of patients, respectively. The postoperative complications were found in 13.1% of patients and one year mortality rate of thymectomy was 6.6%. Conclusion: Regarding to high one year mortality rate of thymectomy in patients of MG in this study, the assessment of the factors related to the mortality and outcome of patients who underwent thymectomy in Iran are necessary.