Abstract The purpose of this study was to measure the average anterior commissure (AC) volume of normal subjects in their 20s or 40s and to determine the effects of gender and age on AC volume. Magnetic resonance brain images were obtained for 93 people in their 20s (46 men, 47 women) and 87 in their 40s (36 men, 51 women). To investigate the effect of gender and age on AC volume, two-way analysis of variance, which used gender (two levels) and age (two levels) as independent variables, was employed. For subjects in their 20s, there was no difference in AC volume between genders, but for those in their 40s, the AC volume of males was less than that of females. There was no difference in AC volume between females in their 20s or 40s; however, the AC volume of men in their 40s was less than that for those in their 20s. There were gender-influenced differences in AC volume changes related to aging.