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Objective: To investigate the clinical and electrophysiological characteristics of myasthenia gravis with thymoma (MGT)., Methods: The clinical and repetitive nerve stimulation (RNS) data of 72 patients with MGT, 36 males and 36 females, and 63 patients with myasthenia gravis without thymoma (NMGT) were analyzed retrospectively., Results: The onset age of 52 of the 72 MGT patients (72.2%) was 35-59. The average onset age of the MGT patients was 39.5, older than that of the NMGT patients (29.4 yrs), and the course of the MGT patients was 13.1 months, shorter than that of the NMGT patients (29.1 months)The attack rate of the males was not significantly different than that of the females. The proportion of generalized presentation type among the MGT patients was 72.8%, higher than that among the NMGT patients (66.7%), particularly concerning the respiratory muscle (20.8% vs. 9.5%). The average time interval between the onset of symptoms and respiratory or bulbar muscle involvement of the NMGT patients were 12 and 7 months respectively, both remarkably shorter than those of the NMGT patients (26.4 and 11.6 months respectively). The abnormal RNS test yield rate of the MGT patients was 86.9%, higher than, however, not significantly that of the NMGT patients (75.0%). 97.2% of the thymoma and mediastinal abnormality could be detected through computed tomography (CT) scan on thymus. The positive rate of AchRab titer of the MGT patients was 50.0%, not significantly different from that of the NMGT patients (52.4%)., Conclusion: MGT is common in middle-aged people, both male and female. The Course is quickly progressive and generalized skeletal muscles, particularly respiratory muscles, are more involved in the MGT patients than in the NMGT patients. RNS study is a sensitive tool to identify MGT. AchRab may not be the specific antibody for recognizing MGT. CT scan is useful in differentiating thymoma preoperatively.