The aim of this study was to investigate whether there is a difference between Alzheimer disease (AD) dementia and pure vascular dementia (VaD) in relation to nitrosative stress levels. We determined serum nitric oxide (NO), oxidized low-density lipoproteins (ox-LDL), and 3-nitrotyrosine levels (3-NT) in healthy elderly individuals (controls, n=15, mean age=73.4±7.9 y), AD patients (n=30; mean age=71.2±12.7 y) and VaD patients (n=20; mean age=75.2±7.5 y). Patients were under anticholinesterase drug therapy. Our results showed that serum NO and ox-LDL levels in AD patients group were significantly higher than in both controls (P<0.001 and P<0.001) and VaD patients (P<0.01 and P<0.001). However, no significant differences in plasma NO and ox-LDL levels were found between VaD and controls. Our study did not reveal significant differences in plasma 3-NT values of dementia patients when compared with controls. There was a significant negative correlation between Mini-Mental State Examination score and serum NO levels in dementia patients (r=-0.349, P<0.01). Serum NO levels were also positively correlated with serum ox-LDL levels (r=0.358, P<0.01). In conclusion, elevation in serum levels of NO was present in probable AD patients but not in VaD patients, and this seems to be related to both ox-LDL levels and cognitive status. Copyright © 2010 by Lippincott Williams & Wilkins.