The purpose of this study is to characterize the spectrum of cerebrospinal fluid (CSF) findings in patients with posterior reversible encephalopathy syndrome (PRES)and determine its associations with severity of edema. In this retrospective cross-sectional study electronic medical reports were screened for patients with PRES. Clinical and laboratory data closest to onset of clinical symptoms were collected. Neuroimaging reports from all patients were categorized according to the presence of vasogenic edema,cytotoxic edema and contrast enhancement. From Jan 1999to Feb 2015, 87 patients with PRES and CSF findings were included. Mean total protein levels were 793 ± 929 mg/l. Median cell counts were 2/μl (IQR 1-4). Eight patients had cell counts[6/μl with a maximum of 41/μl. In 31 patients with extended CSF analysis, mean CSF/serum albuminquotient (QAlb) was 10.1 (IQR 6-17.3). An elevated QAlb (age-adjusted) was found in 74 % of these 31 patients. PRES patients with severe edema had higher mean total protein levels in CSF (mean difference = 407 mg/l; 95 %CI 187-628). Significant correlations were found for edema severity with levels of CSF protein (r = 0.48, p<0.001) as well with QAlb (r = 0.44, p = 0.013). This study shows that total protein in CSF and QAlb are elevated and correlate with severity of edema in PRES patients, whereas pleocytosis was rare in our cohort. This supports the theory that PRES is caused by a dysfunctional blood brain barrier.