Article abstract—Patients with cognitive impairment, particularly as a result of Alzheimer's disease (AD), are at increased risk for falls, but it is unclear how, or if, they differ from normal adults in their balance, gait, or ability to clear an obstacle in their path. Using an optoelectronic camera system, we compared body motions and force output at the feet in patients with probable AD (n = 17) with those in healthy older adults (n = 15) while they stood on a force plate or on a beam attached to the force plate that was either stationary or accelerating. Using the same camera system and comparing this AD group with another group of healthy older adults (n = 24), we observed the AD patients during normal walking and while clearing 25– and 152–mm-high obstacles. None of the AD patients had extrapyramidal signs or musculoskeletal impairments. Compared with healthy older adults, normal walking speed was significantly slower in the AD group (p < 0.0001). While clearing either obstacle, the AD patients were significantly slower in their approach (p p p < 0.02). Moreover, the percent of trials in which a subject made contact with an obstacle was significantly higher in patients with AD (p < 0.005). The AD patients had no evidence of difficulty standing on a flat stationary surface unless the surface suddenly moved. Seven AD patients who were unable to stand on a reduced support surface scored lower in language and memory tasks as well as in caregiver reports of motor coordination than AD patients able to perform the task. In summary, compared with healthy older adults, AD patients walked more slowly, landed more closely to the obstacle after crossing it, and were more likely to contact the obstacle in their path. Independent of extrapyramidal symptoms, these AD patients had no difficulties in balance unless confronted with a more challenging support surface. Changes in obstacle clearance and altered responses to a postural challenge may contribute to the increased fall and fracture risk in AD.