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Radiologic measurements of cortical thickness of the radius and second metacarpal were used to determine bone density in postmenopausal North American Indian (N=34) and Caucasian (N=43) women. The ratio of cortical area to total cross-sectional area was calculated. The mean cortical area ratios, adjusted for number of years postmenopause, were significantly lower in Indian women for both the radius (.60) and metacarpal (.69) compared with Caucasian women (.66 and .76 respectively). Using stepwise multiple regression analysis, the body mass index (kg/m2) and number of years since menopause were identified as significant predictors of radial bone density in Indians. Body mass index was also the most important determinant of metacarpal bone density in Indian women and, contrary to expectations, smoking had a positive effect. Among Caucasian women, both radial and metacarpal bone density decreased with increasing number of years since menopause and with cigarette smoking. Chronologic age, age at menopause, activity level, frequency of consumption of high-calcium foods, and presence or absence of diabetes were not significant predictors of cortical area ratios in either group. The findings from this preliminary study suggest that postmenopausal bone loss may be highly prevalent among American Indians as well as Caucasians.