Numerous studies previously have reported reduced driving performance in people with Parkinson's disease (PD). Few studies to date, however, have examined how specific cognitive difficulties associated with PD impact on specific aspects of driving performance in this population. In this study, the impact of a concurrent task on driving performance was examined. A simulator was used to measure the driving behavior of 18 current drivers with PD and 18 matched controls. The presence of a concurrent task was manipulated between conditions. Results showed that, although groups were similarly affected by the concurrent task on most driving measures, participants with PD were disproportionately affected on operational level driving behavior. It also appears that participants with PD sacrificed concurrent task performance to maintain driving performance. These results further support the hypothesis that cognitive difficulties associated with PD compromise driving performance in this population, even in the mild to moderate stages of the disease.