Whether attempting to pour water into a handheld glass, or simply trying to hold a young child's hand, many activities of daily living require interaction with unpredictable or uncertain mechanical environments. Here we describe a systems identification study that used a planar manipulandum to characterize how hemiparetic stroke survivors adapt reaching movements to novel mechanical environments. By analyzing trial-by-trial variations in hand path kinematics, we found that stroke survivors are less likely than neurologically-intact subjects to adjust motor commands for upcoming movements based on hand trajectory errors experienced on previous trials. This ability is most significantly compromised in subjects with Fugl-Meyer scores ≤ 20. The ability to terminate movement accurately at the desired target was significantly compromised on the impaired side for most stroke survivors. This measure of performance contrasts with the trajectory updating measure in that it did not depend on impairment level. These data suggest that stroke survivors vary in their ability to effectively adapt motor commands based on recent sensorimotor experience. The findings also provide indirect support for the hypothesis that final posture regulation and feedforward trajectory control are complimentary processes that may be differentially compromised following stroke.