Twenty-two cases of purely ocular myasthenia gravis were reviewed to evaluate the long-term effects of thymectomy. Remission rate increased gradually with time (11.8% at 3 years, 23.1% at 5 years, and 33.3% at 10 years). Analysis of factors influencing remission with time showed that patients with short duration of illness attained remission significantly earlier (p = 0.035 at 5-year follow-up). One of 22 patients with purely ocular myasthenia gravis (4.5%) had disease progression. Because ocular myasthenia gravis often progresses to the generalized type and because duration of illness before operation is one of important factors influencing remission, we conclude that thymectomy in the earlier stages of the disease is the preferred treatment for ocular myasthenia gravis, just as for generalized myasthenia gravis.