We report the case of a 62-year-old woman who presented in myasthenic crisis 22 years after radiation- and chemotherapy of an invasive thymoma which occurred during pregnancy. There was no evidence of recurrence of the thymoma at its original site, but an isolated hepatic metastasis was discovered. Biopsy of the mass revealed a spindle cell thymoma, whereas the original histology was that of a mixed round and spindle cell thymoma with moderate lymphocytic infiltration. The patient expired in spite of treatment with steroids, pyridostigmine bromide and plasma exchange on the one hand and cyclophosphamide with adriamycin on the other. To our knowledge, 22 years is the longest reported interval for the appearance of metastatic thymoma and myasthenia gravis after the diagnosis and apparent cure of a primary thymoma. This is also the only reported case of thymoma occurring during pregnancy but not associated with a rapidly fatal outcome.