Although the relationship between myasthenia gravis and thymomas it is well known, with some of myasthenias disappearing after thymectomy, myasthenia may develop after thymoma resection. We present a case of 36 years old man who developed generalized myasthenia 6 years after thymoma surgery; it had been performed tumorectomy, mediastinal fat resection, resection of the anterior wall of left brachiocefalic vein with PTFE patch reconstruction (Masaoka stage III thymoma). After 4 years of corticoid therapy (methylprednisolone) he was operated for steroid cataract. 11 years after resection he is tumor-free and the brachiocefalic vein is functional on CT-scan. Myasthenia after thymectomy is rare but possible after thymoma resection; it is not influenced by association of mediastinal fat resection. The titer of specific auto antibodies and the grade of thymoma invasion are predictive factors for myasthenia development after thymectomy.