The aim of this study was to determine the predictors of long-term survival following surgical resection of thymoma. Forty-one patients with a histologically proven diagnosis of thymoma were evaluated and treated over a 30-year period (1961 to 1991) at our institution. Seven patients (Masaoka stage 111 or IV) were unresectable and were treated by radiotherapy and/or chemotherapy, with an overall 5 year survival of 50%. Thirty-four patients underwent primary surgical excision of the thymoma, most often through a median sternotomy, with 5and 10-year survivals of 90%. Complete excision of the thymoma was achieved in 31 patients with a median survival of 54 months vs. 17 months if incomplete. Independent prognostic factors influencing survival were stage, histology, and patients judged to have a benign thymoma at surgery. Although the thymoma was associated with myasthenia gravis (8 patients) and second primary cancers (8 patients), neither factor was associated with overall survival. We conclude that the most significant predictors of long-term survival of thymoma include complete excision, Masaoka stage I disease, and lymphocytic histology. Multivariate analysis suggested that postoperative chemoradiotherapy may impact on survival.