This study examined the potential of single frequency (50 kHz) BIA for estimation of upper extremity skeletal muscle (SM) mass. Subjects (n = 50) were weight stable adults varying in age (X +/- SD, 51.6 +/- 17 yr) and body mass index (27.2 +/- 5.9 kg/m2). Determinants of arm to arm impedance index (length L; L2/Z) were examined using multiple regression analysis. A good correlation was observed between L2/Z and arm SM estimated by dual-energy X-ray absorptiometry (r = 0.88, p < 0.001). Additional significant model covariates were arm fat mass (p < 0.05), bone mass (p < 0.01), and age (p < 0.001). These findings suggest that upper extremity SM may be rapidly and easily quantified using a simple and inexpensive BIA system combined with appropriate age-adjusted impedance prediction equations.