A 31-year-old woman who presented with a thymoma and myasthenia gravis during pregnancy is reported. The thymoma showed an increase in size during the next 1.5 months. The pregnancy was terminated and a total thymothymectomy was performed with beneficial results. Pathology revealed a lymphoepithelial type with capsule invasion. Thymoma occurring during pregnancy with myasthenia gravis is extremely rare; we therefore review the literature.