BackgroundElectrolyte disturbances and altered renal function have been linked to the prognosis of critically ill patients and recently also of cancer patients. Little is known about the prevalence and prognostic impact of electrolyte and renal disorders in patients with glioblastoma (GBM), the most frequent malignant primary brain tumor. This study aimed to assess electrolyte and renal disorders in GBM patients and evaluate their effect on patients’ outcome.MethodsPatients treated for newly diagnosed GBM between 2005 and 2018 were included. Electrolytes and renal function parameters were assessed preoperatively. Medical records of patients were retrospectively reviewed for demographic and clinical parameters, as well as patients’ survival.ResultsElectrolyte and renal disorders at admission were present in 275 (30.6%) and 544 (60.4%) of 900 GBM patients respectively and were more common in patients with higher age, previous comorbidities and poor initial clinical performance status. In univariate analysis and Kaplan-Meier survival plots, presence of hyponatremia, hypochloremia, hypocalcemia, hyperuricemia and low glomerular filtration rate were associated with poorer survival. Multivariate analysis revealed hypochloremia as an independent prognostic factor for overall (p=0.004) and 1-year (p=0.021) survival. ConclusionsPreoperative electrolyte and renal disorders are common in GBM patients. Of them, only hypochloremia showed a strong association with GBM prognosis, independently of age, sex, extent of resection, clinical performance status, postoperative therapy, and molecular status. Further studies are needed to evaluate the impact of hypochloremia on GBM survival.