A case of pituitary adenoma associated with Rathke's cleft cyst is reported. A 35-year-old woman suffering from visual disturbance, polydipsia-polyuria and amenorrhea galactorrhea was admitted. Since 3 years before admission, she had been administered thyradin under the diagnosis of primary hypothyroidism. Visual acuity was 0.1 on the right and 0.06 on the left, and visual field examination showed bitemporal hemianopsia. Endocrinological study disclosed primary hypothyroidism and moderate hypopituitarism. CT scan showed a low density mass with ring-like enhancement extending in the enlarged sellar cavity and in the suprasellar region. MRI showed a cystic mass in the sellar cavity extending to the suprasellar region, and a solid mass in the left posterior part of the sellar cavity, and the later was thought to be pituitary adenoma. On August 27, 1984, right frontal craniotomy was performed. The right optic nerve was compressed upward, and the right carotid artery laterally with a grayish bulging mass. About 3 ml of grayish colloidal fluid was aspirated and the capsule of the cyst was excised. Postoperative course was uneventful. The visual acuity and visual field defects were improved. Endocrine examination revealed panhypopituitarism. Histologically, the cyst wall was composed of ciliated columnar cells and partially stratified squamous cells. The solid part showed typical pituitary adenoma. There are 5 reports in the literature on the combination of a pituitary adenoma and a Rathke's cleft cyst. In our case, it is thought that the long-standing hypothyroidism induced pituitary adenoma. Therefore, our case with combination of a pituitary adenoma and a Rathke's cleft cyst should be regarded as an occasional coexistence rather than the entity of the transitional cell tumor.