Dietary and lifestyle changes have profound influences on the body mass and nutritional status of individuals living in developed countries. This report used data from a prospective longitudinal study to assess the prevalence of obesity among Sherpa women and to determine which factors were most predictive of it. The body mass index (BMI), energy consumption and expenditures, and physical activity patterns were compared for nonpregnant, premenopausal women living in urban low altitude (n = 216); urban high altitude (n = 56); and rural high altitude (n = 93) settings. Area of residence was highly predictive of the BMI. The mean body weight and BMI were significantly higher for the urban low altitude sample (53.3 kg and 23.5 kg/m , respectively) than for the total high altitude sample (51.4 kg and 21.8 kg/m , respectively). The rural, high altitude sample had the lowest mean body weight (50.1 kg), triceps skinfold (18.5 mm), and BMI (21.3 kg/m ). Although mean BMI was in the range associated with the overall lowest risk to health, distribution of the BMI showed that 29% of the urban low altitude sample were classified obese. The prevalence of obesity was correlated with reduced energy expenditure, not to an increase in consumed calories. Reduced energy expenditures appear to be related to shifts in occupation, access to motorized transportation, and increased affluence, which has allowed Sherpas to hire servants to do manual labor. These data suggest that Sherpa women may potentially be at risk of chronic health problems in the future because of increased adiposity. Am. J. Hum. Biol. 10:519-528, 1998. ยฉ 1998 Wiley-Liss, Inc.