BACKGROUND This randomised, double-blinded, single-centre study prospectively investigated the impact of goal directed therapy and fluid optimization with crystalloids or colloids on perioperative complications in patients undergoing brain surgery. METHODS 80 patients were allocated into two equal groups to be optimised with either crystalloids (n=40) or colloids (n=40). Invasive hemodynamic monitoring and optimization with fluids and vasoactive drugs were used to adjust and maintain mean arterial pressure and cerebral oxygenation within the baseline values (± 20%) and stroke volume variation (SVV) ≤13. Postoperative complications from different organ systems were monitored during the first 15 days after surgery. Hospital stay and mortality were also recorded. RESULTS Crystalloid group received significantly more fluids (p = 0.003) and phenylephrine (p = 0.02) compared to colloid group. This did not have any significant impact on intraoperative or postoperative complications, hospital stay or mortality, where no differences between groups were observed. CONCLUSIONS Either crystalloids or colloids could be used for fluid optimization in brain surgery. If protocolised perioperative haemodynamic management is used, the type of fluid does not have significant impact on the outcome. CLINICAL TRIAL REGISTRATION: Identified as NCT03249298 at www.clinicaltrials.gov KEY WORDS: Brain surgery, fluid optimization, haemodynamic management