The integration of methods to assess daytime physical activity (PA) and sedentary behavior (SB) and nighttime sleep would allow the evaluation of 24-hour daily activity using a single device. Accelerometer devices used to assess daytime PA have not been substantially validated to evaluate sleep. The objective of this study was to use polysomnography (PSG) to validate a commonly used PA accelerometer worn on both wrists and the hip.Seventeen participants (50-75years) completed a single-night in-home PSG recording while concurrently wearing 3 PA accelerometers. Accelerometer devices were worn on each wrist and the hip. Total sleep time (TST), sleep efficiency (SE), and wake after sleep onset (WASO) were compared for each device against PSG. Correlation coefficients estimated measurement agreement. Paired t tests and Bland-Altman plots assessed measurement differences.Between PSG and devices, mean TST ranged from 361.6 to 403.2minutes. Mean SE estimates ranged from 86.9% to 96.9%. Mean WASO estimates ranged from 12 to 51.2minutes. For TST, SE, and WASO hip estimates differed significantly from PSG estimates (paired t tests, TST: P=.03, SE: P<.001, WASO: P< .001). No significant differences were found between wrist accelerometers and PSG estimates of TST, SE, or WASO.PA accelerometer devices worn on either wrist provide valid estimates of TST, WASO, and SE when compared with PSG. Further studies are needed to investigate methods to improve assessment of sleep parameters by PA accelerometer devices to advance device integration and assessment 24-hour activity in populations.