Increasing evidence indicates that inflammation has a substantial role in the pathogenesis and progression of AD. RDW, a measure of heterogeneity in the size of circulating erythrocytes, is associated with inflammatory markers in many numerous diseases. Present study was undertaken to assess the interrelationships between RDW and AD. A total of 197 patients with AD (male/female: 96/101, mean age 76.2 +/- 6.9) and 133 patients as controls with normal cognitive function (male/female: 72/61, mean age 71.68 +/- 5.3) were enrolled in this cross-sectional study. RDW values of all participants were measured. Mini-Mental State Examination (MMSE) and clock drawing tests were performed for cognitive assessment. DSM-IV and NINCDS-ADRDA criteria were used for diagnosis of AD. The mean RDW values were significantly higher in AD group (13.93 +/- 1.1 vs. 13.24 +/- 1.2; p < 0.001) and also a negative moderate correlation between RDW and MMSE was identified (r: -0.453; p < 0.001). After adjusting for confounders, RDW has the strongest association with AD (odd ratio (OR) 1.51, CI = 1.10-2.07). In present study RDW levels were significantly increased in patients with AD. Whereas elevated RDW value is usually considered as a novel biomarker of inflammation, the results of our study may support the role of inflammation in pathophysiology of AD. Furthermore the correlation of RDW with poorer cognition status suggests that it may be used as a marker of AD severity. (C) 2012 Elsevier Ireland Ltd. All rights reserved.