This study investigated the effect of gender on age-related changes in muscle thickness (Mt) in the elderly, with relation to the differences due to the location of muscle groups. Mt values at the forearm, upper arm anterior and posterior, abdomen, subscapular, thigh anterior and posterior, and lower leg anterior and posterior were determined using ultrasonography in 188 men and 204 women aged 65 to 79 yrs. The men had thicker muscles than the women, with a greater relative difference in the upper limb and trunk compared to the lower limb muscles. For the men, Mt values at the upper limb, thigh and abdomen were negatively correlated to age (r =-0.330 to -0.214, p<0.05). For the women, only the Mt at the thigh anterior showed a significant negative correlation with age (r =-0.346, p<0.05). At the thigh anterior, there was no significant difference between both genders in the slope of the regression line for the relationship between age and percentages of Mt to the mean value for the subjects aged 65 to 69 yrs of men and women, respectively, suggesting that the rate of the age-related loss of Mt at this site was independent of gender. These results were the same even when Mt was expressed as the value relative to (body mass)^1/3, calculated to normalize the influence of the difference in body mass. The findings obtained here indicated that, in an age span from 65 to 79 yrs, 1) gender difference in muscle thickness was more apparent in the upper limb and trunk than in the lower limb muscles, and 2) men showed significant age-related losses in muscle thickness at more body sites as compared to women, especially at the upper limb and abdomen.