Post operative complications after pituitary tumour surgery vary according to procedure. There are several surgical procedures being done such as transcranial, transsphenoidal microsurgical and transsphenoidal endoscopic approaches. One of the commonest complications is diabetes insipidus (DI). Our main objective was to find out the incidence of diabetes insipidus in post operative period among patients undergoing surgical intervention for pituitary tumour in our institute. The presence of diabetes insipidus in the postoperative period was established by measuring serum Na+ concentration, hourly urine output and urinary specific gravity to find out the incidence of diabetes insipidus in postoperative period in relation to age, gender, tumour diameter, function of tumour (i.e., either hormone secreting or not) and operative procedure used for surgical resection of pituitary tumor. As it is the most common postoperative complication so, in this study we tried to find out how many of the patients develop diabetes insipidus in postoperative period following surgical resection of pituitary tumour. This cross sectional type of observational study was carried out in the department of Neurosurgery, BSMMU from May 2014 to October 2015 on 33 consecutive patients who underwent surgical intervention for pituitary tumour for the first time. Data was collected by using a data collection sheet. The incidence of diabetes insipidus was found 23.1% of patients in <30 year age group, 38.5% of patients in 31-40 year age group and 38.5% of patients in ≥40 year age group (p=0.764). In case of distribution of patients according to gender 38.5% of male and 61.5% of female developed diabetes insipidus (p=0.073). Regarding tumour size 30.8% and 69.2% of patients developed diabetes insipidus having tumour diameter <30mm and ≥30mm respectively (p=0.590). In case of operative procedure 69.2% of patients developed diabetes insipidus who was operated by transsphenoidal endoscopic approach, 23.1% and 7.7% of patients developed diabetes insipidus who underwent pituitary tumour resection through transsphenoidal microscopic approach and transcranial microscopic approach respectively (p=0.432). 17.6% of patients develop DI having functioning pituitary macroadenoma and 62.5% of patients develop DI having nonfunctioning pituitary macroadenoma. This observational study has been performed to find out the incidence of diabetes insipidus. Incidence of postoperative DI is more at or around the age of 40 years. It is slightly predominant in female. Most of the patients manifest DI in the first 24 hours of surgical intervention. Incidence of DI is low among patients having functioning pituitary macroadenoma.