[en] A 75 year old woman was found to have a posterior cerebellar lesion which after surgical removal was shown to be a meningioma. Her postoperative course was complicated by a MRSA meningitis and on day 23 after resection, a polyuria up to 11.7 1/24 h became apparent. The diagnosis of cerebral wasting syndrome (CSWS) was made based on biological and clinical features such as an excessive natriuresis (143 mmol/l) resulting in hyponatremia (130 mmol/l) and an osmolarity higher in urine than in blood. A low central venous pressure and a low wedge pressure confirming a volumic depletion indicated the diagnosis of CSWS. This syndrome has marked similarities with the Inappropriate Secretion of Antidiuretic Hormone Syndrome (SIADH) in terms of biological finding with regards to clinical context and presentation. Without an adequate assessment, a patient with CSWS may be misdiagnosed as SIADH. However recognition is important, as water restriction which is part of SIADH treatment, is detrimental to patients with CSWS and can possibly be lethal.