Dilated pupils after craniotomy are commonly caused by increased intracranial pressure. Most patients have dilated pupils due to intracranial hematoma compressing the nerves after craniotomy, and some have dilated pupils due to damage to brain tissue from craniotomy, causing malignant swelling of brain tissue and squeezing the brainstem. There are also pupil dilatation caused by damage to the brainstem or the motoneurotic nerve during surgery. Because the injury site is different, different symptoms appear. For the above cases, it is important to pay attention to review the cranial CT, as well as to understand the cause from the surgeon.