Patient registers on myasthenia gravis (94 patients) and multiple sclerosis (991 patients) from a population of 1.5 million were reviewed to find patients with both diseases. Seven potential candidates were found, but both diagnoses were confirmed in 2 women only. The first patient had also iritis, the second patient had, besides MG and MS, bronchial asthma and polyarthritis. Both neurological diseases had a relatively mild clinical course. Thymectomy relieved MG symptoms in both patients. Cerebrospinal fluid studies during the follow-up indicated immunoactivation within the central nervous system. Changes in cellular immunity were also noted. The HLA types were different. The combination of these two diseases appears to be more common than expected.