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Human gait is precisely and continuously adapted in order to negotiate obstacles safely and without excessive modulations to lower limb trajectories. To investigate obstacle clearance, unimpaired healthy adult subjects (6 male and 6 female) were videotaped stepping over an obstacle adjusted to 10%, 25%, and 40% of leg length. Lead foot clearance was relatively uninfluenced by obstacle height whereas trail clearance increased systematically. As height increased the lead foot crossed earlier in the normalised stride but crossing distance remained at about 80% of normalised stride length. Trail foot clearance increased with height while crossing time was unchanged. Discussion of these findings focussed on a motor control process in which information from the visually-guided lead foot might be used to control trail foot trajectory.