Thymoma and myasthenia gravis are frequently associated, However, the nephrotic syndrome has been observed rarely in association with a thymoma. We report a 56-year-old patient with a history of thymectomy 3 years ago and myasthenia gravis who developed nephrotic syndrome under immunosupressive treatment. The pathogenesis is not clear and the role of a disorder of T-cell function and of circulating cytokines is discussed.