Objectives: To evaluate (1) the influence of rhythmic cues on gait interference during a functional activity and (2) the relationship of clinical symptoms to gait interference. Design: Repeated-measures study. Setting: Participants' homes. Participants: Twenty subjects with idiopathic Parkinson's disease (PD) and a control group of 10 age-, sex-, and education-matched subjects. Interventions: Subjects performed a simple functional task that included a walking component and a dual-motor task. The functional task was performed with and without external rhythmic (auditory and visual) cues. Main Outcome Measures: Walking speed, mean step length, and step frequency were compared during trials of the tasks. In addition, tests of cognitive executive function (Hayling and Brixton tests), anxiety and depression (Hospital Anxiety and Depression Scale), and fatigue (Multidimensional Fatigue Inventory) were undertaken. Results: The use of auditory cues during a dual task involving gait reduced the interference effect on the task; significant increases in step length were observed in PD subjects (P=.018), representing an increase of 19%. Conclusions: External auditory cues may be useful in reducing interference and maintaining gait performance during more complicated functional activities. Clinical symptoms, such as depression and fatigue, could influence the ability to focus attention and may increase gait interference during the performance of complex tasks, with subsequent implications for functional walking and safety. © 2005 by American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.