OBJECTIVE: Diabetes insipidus (DI) is a well-known complication of transsphenoidal pituitary adenoma surgery. However, the risk factors for DI after transcranial surgery have not been clarified. In this study, the clinical parameters for predicting DI after transcranial surgery were investigated. METHODS: The perioperative records of 90 patients who underwent transcranial (TC) surgery at the authors' institution between November 2011 and March 2013 were chosen from 1657 patients with pituitary adenoma and retrospectively analyzed. The degree of deformation of the third ventricle and hypothalamus were assessed by preoperative magnetic resonance imaging. RESULTS: Immediate postoperative DI was found in 30 patients (33.3%). Persistent DI was noted in 11 patients (12.6%). Compared with patients in the nonpostoperative DI group, those with postoperative DI had a higher degree of deformation of the third ventricle and hypothalamus (P < 0.001). In a binary logistic regression analysis, the degree of deformation of the third ventricle and hypothalamus (odds ratio [OR], 3.079; 95% confidence interval [CI], 1.600-5.925; P = 0.001) had a significant positive correlation with immediate postoperative DI, as well as postoperative hemorrhage (OR, 6.235, 95% CI, 1.457-26.689; P = 0.014). Postoperative hemorrhage (OR, 4.363; 95% CI, 1.021-18.647; P = 0.047) showed a positive correlation with permanent DI, as well as the degree of deformation of the third ventricle and hypothalamus (OR, 2.336; 95% CI, 1.005-5.427; P = 0.049). CONCLUSIONS: The degree of deformation of the third ventricle and hypothalamus assessed by preoperative magnetic resonance imaging may help to predict postoperative DI. Postoperative hemorrhage might increase the incidence of postoperative DI, whether it is immediate postoperative DI or permanent DI.