Between 1977 and 1979, 12 consecutive patients with myasthenia gravis who were over the age of 55 years were treated by thymectomy. In all, their conditions improved clinically; 11 of the 12 became free of the generalized features of myasthenia gravis. Nine patients required no further medication. Acetylcholine-receptor antibody titers did not change significantly. Although five patients had atrophic thymus glands, their conditions also improved. We conclude that (1) thymectomy is a safe and effective therapy for patients with myasthenia gravis who are over the age of 55 years; (2) steroids and anticholinesterase agents are not essential in the management of late-onset myasthenia gravis; and (3) reduction in acetylcholine-receptor antibody titer is not essential for beneficial clinical response.