Although brain development is most active during the intrauterina period of life, the processes of myelination and arborization affect the structure of the brain throughout childhood and adolescence. Brain development is also very active in the early years of a child's life, and continues to be so for approximately 15 years after gestation. Volumetric changes in the brain are effected by sex. Understanding the variability of human brain volume during development is important for the interpretation of childhood neuroimaging studies. Hence the aim of this study is to determine the effects of sex difference on brain volume (BV), lateral ventricle volume (LV) and the ratio of brain volume and lateral ventricle volumes as a percentage (RLBV%) of 90 healthy children between the ages of 6-17 according to their sex with MRI. These children were divided into three age groups of 6-9, 10-13 and 14-17 also BV, LV were calculated using the Cavalieri principle, which is classified as a stereological method and than RLBV% were calculated.