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Background  The coexistence of two histologically distinct neoplasms in the same area without histological admixture or an intermediate cell population zone represents a rare tumor type called collision tumor. Collision tumor of pituitary adenoma and meningioma has been reported years later following irradiation to pituitary adenoma. However, collision tumor of pituitary adenoma and meningioma in absence of irradiation therapy is extremely uncommon. Case Description  We report an unusual case of collision tumor involving diaphragma sella meningioma and pituitary adenoma in a 50-year-old lady without prior radiation therapy. She presented with visual blurring and impaired field of vision. Her preoperative magnetic resonance imaging (MRI) was suggestive of pituitary adenoma. Total excision of the lesion was performed through endoscopic transsphenoidal route. Histological diagnosis was consistent with collision tumor of pituitary adenoma and meningioma. Conclusion  Collision tumor comprising of nonfunctioning pituitary adenoma and meningioma is extremely rare. Preoperative MRI may not always be able to distinguish these histologically distinct neoplasms. Hence, histopathological examination is necessary to establish the diagnosis. Endoscopic transsphenoidal approach may suffice in excision of these collision tumors. Close follow-up is necessary to detect tumor recurrence. Though the association of these tumors can be coincidental, casual relationship between the occurrence of collision tumors cannot be totally excluded., Competing Interests: Conflict of Interest None declared., (Asian Congress of Neurological Surgeons. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. ( https://creativecommons.org/licenses/by-nc-nd/4.0/ ).)