Background: Cerebral salt wasting syndrome (CSWS), syndrome of inappropriate antidiuretic hormone secretion (SIADH) and diabetes insipidus (DI) are frequently found in postoperative neurosurgery. Purpose: To identify these syndromes following neurosurgery. Method: The study included 30 patients who had been submitted to tumor resection and cerebral aneurysm clipping. Sodium levels in serum and urine and urine volume were measured daily up to the 5(th) day following surgery. Plasma arginine vasopressin (AVP) was measured on the first, third and fifth days post-surgery. Results:CSWS was found in 27/30 patients (90%), in 14 (46.7%) of whom it was associated with a reduction in the levels of plasma AVP (mix syndrome). SIADH was found in 3/30 patients (10%). There was no difference between the two groups of patients. Conclusion: CSWS was the most common syndrome found, and in half the cases it was associated with DI. SIADH was the least frequent syndrome found.653B745751