In this case report, data are presented from a patient, who suffered from a severe subarachnoid haemorrhage and was admitted to the neuro-intensive care unit, where the use of cerebral microdialysis (CMD) allowed the detection of a severe mismatch between cerebral and systemic glucose levels and compromised cerebral metabolism despite systemic glucose values within the normal range. The established CMD monitoring allowed subsequent titration of insulin respecting acceptable cerebral and systemic glucose levels.