SUMMARY: The corpus callosum (CC) includes the majority of fibers linking the two brain hemispheres. Several cross sectional studies showed an association between callosal atrophy and malfunction and neurodegenerative diseases, which may play a role in their pathological manifestations. As a result, the accurate quantification of the corpus callosum is important to have normative values according to sex, age and ethnicity. The purpose of this study is to determine the size of CC in patients suffering from multiple sclerosis, and compare it to CC size in healthyindividuals. Midsagittal size of CC were recorded prospectively from 404 routine MR brain examinations in normal individuals. The internal skull surface was measured to calculate CC/ internal skull surface ratio. Two groups of patients were studied: 200 (100 male /100 female) healthy individuals and 204 (101 males/103 females) with multiple sclerosis (MS). Mean surface area of CC in controls was 6.58±1.04 cm2 and there was no significant difference between males and females (P< 0.627). CC/ internal skull surface ratio was 4.44±0.77 %. MS patients showed a significant decrease in CC size compared to normal controls. Using MR imaging, we measured the mean sizes of the various portions of the CC in normal individuals, in addition to MS patients; these values may provide a useful basis to determine changes occurring in CC structures.