Turning during walking is frequently problematic in Parkinson's disease (PD). The spatiotemporal characteristics of footstep adjustments used to turn 60 and 120 degrees were examined in 10 people with PD and 10 age, gender- and height-matched control subjects, using three-dimensional motion analysis. Control subjects used a recognizable pattern of spatial and temporal footstep modulations to turn. Participants with PD demonstrated significant differences in almost all variables. They (1) failed to turn as far as their peers; (2) showed a similar but scaled-down pattern of spatial adjustments to turn; (3) used shorter strides when walking, with exaggerated reductions when turning; and (4) demonstrated small but significant temporal differences in step time adjustments. Group differences were more marked for the larger turn. Spatial results, interpreted in light of hypothesized basal ganglia dysfunction, are consistent with a normal motor command but impaired ability to maintain movement amplitude. Differences in adjustment of step time to turn may reflect impaired locomotor timing control in subjects with PD during challenging gait tasks.