Collision tumors of the sellar region are relatively uncommon and consist mainly of more than one type of pituitary adenoma or a cyst or cystic tumor. The association of a pituitary adenoma and a craniopharyngioma is particularly rare. This study describes a rare occurrence in which a pituitary adenoma and a craniopharyngioma coexisted in the sellar region. The case involves a 47-year-old woman who underwent transsphenoidal surgery with subtotal tumor resection and reoperation using an interhemispheric transcallosal approach for total microsurgical resection of the tumor because the visual acuity in her left eye had re-deteriorated. Histopathological and immunohistochemical examinations of the excised tissue revealed a pituitary adenoma in the first operation and a craniopharyngioma in the second operation. Retrospective analysis found the coexistence of a pituitary adenoma and a craniopharyngioma, known as a collision tumor. Instead of the transsphenoidal approach, a craniotomy should be performed, to explore the suprasellar region.