We report a rare case of intratumoral hemorrhage during postoperative radiotherapy for pituitary adenoma. A 57-year-old Asian male, complaining of long-standing eye strain, underwent a medical checkup of the brain. Magnetic resonance imaging showed a multicystic giant pituitary adenoma. The patient underwent an endoscopic endonasal transsphenoidal partial removal of the adenoma to provide optic pathway decompression and got relief from the visual symptoms. Just before completion of the postoperative radiotherapy for residual adenoma, the patient developed right hemiparesis, mild motor aphasia, and right oculomotor palsy. A cranial CT scan showed intratumoral hemorrhage into the intratumoral cyst. The patient therefore had to undergo three additional craniotomies for evacuation of cyst contents over the next 8 months. The follow-up MRI at 11 months after the initial hemorrhage showed that the new oozing of blood in the intratumoral cyst was still appearing. Intratumoral hemorrhage is a rare, albeit life-threatening, complication of pituitary adenoma. We reviewed relevant literature and suggested that the cystic component in pituitary adenoma could be a key pathogenesis of this rare complication. In conclusion, we suggest that it may be necessary to realize that cases which have cystic giant pituitary adenoma may cause hemorrhage by chance with the foreseeability.