Thymectomy is a therapeutic option for patients with myasthenia gravis with moderate to severe disability. To document the efficacy of thymectomy coupled with medical therapy to treat this disease and to identify clinical factors that influence outcome, the clinical courses of all 46 patients (12 male and 34 female; mean age, 30 +/- 16 years) with myasthenia gravis who underwent thymectomy through a median sternotomy at a single institution over a 21-year period were reviewed. Clinical staging was determined preoperatively, at 1 month, 6 months, and 12 months postoperatively, and at last follow-up (mean time, 75 months postoperatively) using the Oosterhuis classification. Changes in severity of illness were graded as "deteriorated," "unchanged," "improved," or "much improved." Preoperative Oosterhuis classification was 3.3 +/- 1.1 and at last follow-up, 1.4 +/- 1.2 (p = 0.022). At last follow-up, 40 patients (87%) were in the improved or much improved category, and 6 patients were in the deteriorated or unchanged category. Status at 1 month, 6 months, and 12 months after operation predicted outcome at last follow-up visit (p = 0.007, p = 0.005, and p = 0.001, respectively). Clinical factors that positively influenced outcome were age less than 45 years (p = 0.004), female sex (p = 0.0309), and preoperative stage (p = 0.021).