Aneurysmal subarachnoid hemorrhage (aSAH) is a devastating event. Following the bleeding, a number of pathophysiological changes and clinical factors determine outcome. Not surprisingly, attempts to predict outcome based on a single factor have failed. The neurological status graded at admission to hospital and distributions of the blood on CT are the strongest predictors. There is evidence that cerebrospinal fluid (CSF) proteins may serve as markers of the extent of brain damage. The present study is focused on the light unit of neurofilament protein (NFL), previously not evaluated in aSAH. Lumbar puncture (LP), neurological grading according to World Federation of Neurological Surgeons (WFNS) and neurological examination according to the National Institute of Health Stroke Scale (NIHSS) were performed in 48 consecutive patients with aSAH 10-14 days after the hemorrhage. CSF-NFL concentrations were analyzed using an ELISA. Outcome was assessed after 1 year and categorised according to the extended Glasgow Outcome Scale (GOSE). A significant correlation between CSF-NFL and GOSE was detected at follow up after 1 year. CSF-NFL also correlated with WFNS and NIHSS on the day of the lumbar puncture. CSF-NFL is a biochemical marker of brain damage correlating to neurological status and long-term outcome after aneurysmal subarachnoid hemorrhage.