The body mass index (BMI) has been promoted as a useful indicator for chronic energy deficiency, and to a lesser extent to indicate obesity. For the growing sector of elderly in developing countries, such as Indonesia, both issues are taking on public health relevance. The aging process leads to a progressive loss of height, and questions have been raised as to the appropriate value to include in the denominator of the BMI formula, WT(kg)/HT(m2), when applied in this age-group. The armspan has been advanced as a surrogate for height, correcting for the lifelong loss of stature. In a data-set from 69 elderly in Indonesia, 36 women and 33 men, aged 60 to 69 y, we have examined the interrelationships of height and armspan. The correlation coefficient for the regression of the two measures were r = 0.83 and r = 0.81 (p < 0.001), for women and men, respectively. Substituting the armspan term in the denominator to compose a Body Mass using Armspan (BMA) Index, we observe for this population a 32% increase in estimates for Chronic Energy Deficiency (CED) for women and 24% increase in estimates of CED for men. Corresponding estimates for obesity rates declined by 45% and 81% respectively. The senescent changes in stature raise important questions for our capacity to estimate prevalences of body composition disorders in the older population.