Older adults undergoing rehabilitation may have limited mobility, slow gait speeds and low levels of physical activity. Devices used to quantify activity levels in older adults must be able to detect these characteristics.To investigate the validity of the Positional Activity Logger (PAL2) for monitoring position and measuring physical activity in older inpatients (slow stream rehabilitation).Twelve older inpatients (≥65 years) underwent a 1-hour protocol (set times in supine, sitting, standing; stationary and moving). Participants were video-recorded while wearing the PAL2. Time spent in positions and walking (comfortable and fast speeds) were ascertained through video-recording analysis and compared with PAL2 data.There was no difference between the PAL2 and video recording for time spent in any position (P-values 0.055 to 0.646). Walking speed and PAL2 count were strongly correlated (Pearson's r = .913, P < .01). The PAL2 was responsive to within-person changes in gait speed: activity count increased by an average of 52.47 units (95% CI 3.31, 101.63). There was 100% agreement for transitions between lying to sitting and < 1 transition difference between siting to standing.The PAL2 is a valid tool for quantifying activity levels, position transitions, and within-person changes in gait speed in older inpatients.