Keywords:Stereology Cavalieri principle Planimetry Magnetic resonance imaging Brain Intra-rater variation ARTICLE INFO ABSTRACTMeasurement of brain volume is regarded as an objective marker of neurodegenerative diseases. The purpose of this study is to evaluate intra-rater variation for the estimation of volume of cerebral structures using the Cavalieri principle on magnetic resonance (MR) images to determine its reproducibility. The MR images of 30 cases were analyzed using the same standard protocols of the Cavalieri principle in two sessions with one month intervals. The structural MR images were analyzed using the ImageJ software by the same observer. The planimetry and threshold process was used for the cut surface area assessments. The volume of hemispheres, total brain, gray and white matters were and lateral ventricles estimated by means of the multiplication of cut surface are by the section interval. The same sections were used in both sessions. The results of two sessions were compared using Wilcoxon Signed Rank test. The mean total brain, right and left hemispheres volumes of first session were 1089.53, 544.82 and 544.71cm 3 , respectively. The mean total brain, right and left hemispheres volumes of second session were 1086.62, 543.99 and 542.63cm 3 , respectively. There was no statistically significant difference between the data (p>0.05). The mean total gray and white matters volumes were 553. 55, 535.98 and 549.32, 537.31cm 3 for the first and second sessions, respectively. There was no statistically significant difference for the gray and white matters results (p>0.05). Our results showed that the reproducibility of the obtained data is good. The volume of cerebral structures could be estimated using the Cavalieri principle on MR images for comparative studies. We are planning to evaluate inter-rater difference in advance.