Clinicians are in need of valid and objective measures of postural sway. Accelerometers have been shown to be suitable alternatives to expensive and stationary force plates. We evaluated the test-retest reliability and balance task discrimination capability of a new wireless triaxial accelerometer (YEI 3-Space Sensor). Four testing conditions (eyes open or closed, while on a firm or compliant surface) were used to progressively challenge the static balance of 20 healthy male (n = 8) and female (n = 12) older adults (mean age 81 ± 4.3 y). Subjects completed 2 blocks of three 30-second trials per condition. The accelerometer was positioned on the lower back to acquire mediolateral (M-L) and anterior-posterior (A-P) accelerations. Intraclass correlation coefficients were all good to excellent, with values ranging from .736 to .972 for trial-to-trial and from .760 to .954 for block-to-block. A significant stepwise increase in center of mass acceleration root mean square values was found across the 4 balance conditions (F[1.49, 28.26] = 39.54, P < .001). The new accelerometer exhibited good to excellent trial-to-trial and block-to-block reliability and was sensitive to differences in visual and surface conditions and acceleration axes.