This study was conducted to evaluate the efficacy of debulking surgery in the treatment of locally advanced but operable malignant thymoma.We reviewed 43 cases with incompletely resected stage III and IVa malignant thymoma managed between January 1987 and December 2002.Twenty-two had stage III and 21 had stage IVa disease. Maximal debulking was performed in 15 patients, nine with stage III and six with stage IVa disease. Nine patients also had myasthenia gravis (MG). Using univariate Kaplan-Meier analysis, we found that maximal debulking surgery, RT, and with the presence of MG were associated with better survival. Debulking resulted in a better outcome than non-debulking surgery (mean survival: 106 months vs 57.2 months). After adjustment with multivariate analysis, RT and MG were both associated with better survival. CT did not appear to be beneficial for advanced thymoma.RT is independently associated with a better outcome in locally advanced thymoma. Debulking surgery apparently allows for a better response to RT.