Background. A reduced capacity to modify gait to the environment may contribute to the risk of falls in people with poststroke foot drop using an ankle-foot orthosis. Objective. This study aimed to quantify their capacity to restore steady gait after a step modification. Design. This was a cross-sectional, observational study. Methods. Nineteen people in the chronic phase (>6 months) after stroke (mean age=55.0 years, SD=10.1) and 20 people of similar age (mean age=54.6 years, SD=12.0) who were able-bodied were included. Participants were instructed to avoid obstacles that were suddenly released in front of the paretic leg (stroke group) or left leg (control group) while walking on a treadmill. Outcomes were success rates of obstacle avoidance as well as post-crossing step length, step duration, hip flexion angle at foot-strike, and peak hip extension of the steps measured within 10 seconds following obstacle release. Results. Success rates of obstacle avoidance were lower for people poststroke. Moreover, their first post-crossing step length and duration (ie, the nonparetic step) deviated more from steady gait than those of people in the control group (ie, the right step), with lower values for people poststroke. Similar deviations were observed for post-crossing hip flexion and extension excursions. Limitations. People poststroke were relatively mildly impaired and used an anklefoot orthosis, which may limit the generalizability of the results to other populations poststroke. Conclusions. People with poststroke foot drop using an ankle-foot orthosis had reduced gait adaptability, as evidenced by lower success rates of obstacle avoidance as well as an impaired capacity to restore steady gait after crossing an obstacle. The latter finding unveils their difficulty in incorporating step modifications in ongoing gait. © 2014 American Physical Therapy Association.