A 25‐year‐old man with myasthenia gravis and a non‐Hodgkin lymphoma stage III B involving the thymus, is reported. The association myasthenia gravis and non‐Hodgkin lymphoma has not been described previously. Treatment with chlormetin, vincristine, procarbazine, prednisone (MOPP) resulted in complete remission of both the myasthenic symptoms and the malignant lymphoma.