Objective To examine the validity of 5 robot-based assessments of arm motor function poststroke. Design Cross-sectional study. Setting Outpatient clinical research center. Participants Volunteer sample of participants (N=40; age, >18y; 3–6mo poststroke) with arm motor deficits that had reached a stable plateau. Interventions Not applicable. Main Outcome Measures Clinical standards included the arm motor domain of the Fugl-Meyer Assessment (FMA) and 5 secondary motor outcomes: hand/wrist subsection of the arm motor domain of the FMA, Action Research Arm Test, Box and Block test (BBT), hand motor subscale of the Stroke Impact Scale Version 2.0, and Barthel Index. Robot-based assessments included wrist targeting, finger targeting, finger movement speed, reaction time, and a robotic version of the BBT. Anatomical measures included percent injury to the corticospinal tract (CST) and extent of injury of the hand region of the primary motor cortex obtained from magnetic resonance imaging. Results Participants had moderate to severe impairment (arm motor domain of the FMA scores, 35.6±14.4; range, 13.5–60). Performance on the robot-based tests, including speed (r=.82; P<.0001), wrist targeting (r=.72; P<.0001), and finger targeting (r=.67; P<.0001), correlated significantly with the arm motor domain of the FMA scores. Wrist targeting (r=.57–.82) and finger targeting (r=.49–.68) correlated significantly with all 5 secondary motor outcomes and with percent CST injury. The robotic version of the BBT correlated significantly with the clinical BBT but was less prone to floor effects. Robot-based assessments were comparable to the arm motor domain of the FMA score in relation to percent CST injury and superior in relation to extent of injury to the hand region of the primary motor cortex. Conclusions The present findings support using a battery of robot-based methods for assessing the upper extremity motor function in participants with chronic stroke.