Objective To evaluate the long-term outcome of thymectomy combined with steroid therapy for myasthenia gravis (MG) with thymoma.Methods Fifty-two MG patients with thymoma (35 males, 17 females) treated with thymectomy combined with steroid therapy underwent a retrospective study during a follow-up period of 1 to 20 years (mean 4.5±3.6) after thymectomy in order to evaluate the long-term effective rate and survival rate. Five cases had ocular MG, and 47 had generalized MG (90.3%). The patients at onset from 8 to 61 years (mean 38.5±12.7). All patients were given steroid therapy before and after thymectomy. At the start of therapy, prednisone was given 30 mg to 60 mg daily. This dose was maintained until obvious improvement was found, after which prednisone dosage was gradually tapered to 10 mg to 20 mg daily as a maintenance dose and continued for 1 to 2 years. In all these patients the extended thymectomy was performed by median sternotomy, if possible, a complete resection of the thymoma and the thymic gland, including perithymic fat tissue was given. The survival rate after thymectomy was calculated employing the Kaplan-Meier's method.Results The long-term effective rate was 88.5% (46/52). In the 46 survivors, 8 of them (15.4%)obtained complete remission (patients asymptomatic without any therapy for at least 6 months), 29 of them (55.8%) had pharmacological remission (patients asymptomatic still on low dose corticosteroids or anticholinesterases), 9 of them (17.3%) had marked improvement (stable improvement of myasthenic signs corresponding to a decrease of 2 points on the functional scale of Oosterhuis et al). Six patients (11.5%) died during the observation period. Two of them died in one year after thymectomy; 4 of them died during the follow-up period in from 1 to 20 years. The causes of death after surgery were: thymoma relapse and metastasis in 2 patients, heart failure after operation in 1, myocardial infarction in 1, myasthenic crisis in 1 and digestive tract hemorrhage due to high dose steroid in 1. The mortality of patients with invasive thymoma was 23% (3/13); the mortality of patients with noninvasive thymoma was 7.7% (3/39). The 1-year survival rate after operation was 96.2% (50/52), 3-year survival rate 91.4% (32/35), the overall 5-year survival rate 85.7% (18/21), the overall 7-year survival rate 77.8% (14/18) and the overall 10-year survival rate 33.3% (3/9).Conclusions The long-term therapeutic results of thymectomy combined with steroid therapy were good for myasthenia gravis patients with thymoma. Our retrospective study results showed that thyectomy combined with steroid therapy played an important role in decreasing mortality and increasing remission rate.