 The purpose of this 5-year trial is to determine if the surgical procedure, extended transsternal thymectomy ETTX, combined with prednisone therapy is more beneficial in treating individuals with non-thymomatous MG than prednisone therapy alone. More specifically, this study will determine 1 if ETTX combined with prednisone results in a greater improvement in myasthenic weakness, compared to prednisone alone; 2 if ETTX combined with prednisone results in a lower total dose of prednisone, thus decreasing the likelihood of concurrent and long-term toxic effects, compared to prednisone alone; and 3 if ETTX combined with prednisone enhances quality of life by reducing adverse events and symptoms associated with the therapies, compared to prednisone alone. 