: A 23-year-old non-diabetic woman presented to our emergency room with progressive headache. She was diagnosed with craniopharyngioma and received tumor resection. Her blood glucose level was within the normal limit before surgery, and she had no family history of diabetes. Three months after the surgery, acute hyperosmolar hyperglycemic state developed. After 4 months of follow-up, her diabetes persisted but improved with oral antidiabetic drugs. This is the third case report of diabetes developing several months after craniopharyngioma tumor resection. The possible mechanisms of cranipharyngioma or its surgery inducing diabetes mellitus are hypothalamic obesity or hypothalamic damage. The degree of hypothalamic damage before the operation is predictive of diabetes development, and blood glucose level monitoring is important for these patients.