Differential bone mass at various skeletal sites, which may be due to mechanical stress exerted by the muscles attached to the bone, has been demonstrated for athletes who exert one limb more than the other. The question arises as to whether this bilateral asymmetry extends to the two sides of the same bone with different muscular attachments. The objectives of this study were to ascertain whether the radial and ulnar sides of the second metacarpal have similar cortical thickness and determine if bone mass decreases equally with age on the radial and ulnar sides. Hand-wrist radiographs were obtained from 201 male and 191 female Caucasian participants of the Baltimore Longitudinal Study of Aging. Differences between radial and ulnar cortical thickness within age groups were tested with Student's t-test and between age groups using analysis of variance. RAdial cortical thickness of the second metacarpal was found to be 11-12% greater in men and 10-12% greater in women than ulnar cortical thickness in both the left and right hands. Age-related changes in radial cortical thickness were evident in both sexes. In men, radial cortex decreased linearly from age 40 to 89. For women, there was a sharp decline in radial thickness from age 50 to age 60. Ulnar cortical thickness declined from age 50 to 60 for women only. Muscle attachment along the radial length of the second metacarpal may influence the accumulation of bone mass on the radial side at younger ages while muscle disuse may precipitate the loss of bone preferentially from the radial side.