Oxidative stress may be involved in pathogenesis of neurodegenerative diseases. We aimed to measure MDA, NO, 8-OHdG and TAC, SOD and CAT levels in the Alzheimer disease, Parkinson disease and vascular dementia, and evaluate oxidant and antioxidant status in these diseases. Oxidative stress parameters were measured in 20 patients with vascular dementia, 20 patients with the Alzheimer disease, 20 patients with the Parkinson disease and 20 matching controls. MDA, NO and TAC were assayed with spectrophotometric methods. 8-OHdG was quantitated by the Elisa method. SOD and CAT were assayed with colorimetric methods. MDA, NO, 8-OHdG and SOD levels in total patient group were higher (p = 0.039, 0.041, 0.021 and 0.045, respectively), while TAC levels were lower (p = 0.010) as compared with controls. When compared to controls, the following were higher: MDA in the Parkinson disease (p = 0.036); NO in the Alzheimer disease (p = 0.028). However, TAC in the Alzheimer disease (p = 0.024) were lower. We observed negative correlations between TAC and MDA in the Parkinson disease (r = -0.496, p = 0.026); between SOD and 8-OHdG in the Alzheimer disease (r = 0.526, p = 0.017).