Objective. The objective of this study was to determine how Parkinson's disease (PD) affects functional cognition as assessed by the Complex Task Performance Assessment (CTPA) and to examine the associations of CTPA performance with other indicators of executive function in people with PD. Method. Volunteers with PD without dementia (n = 20) and community control participants (n = 19) completed neuropsychological testing, patient-reported outcome measures, and the CTPA. Results. There were no group differences for CTPA performance accuracy; however, the PD group took longer to complete the CTPA than did the control group. In the PD group, inefficient CTPA performance correlated with poorer cognitive flexibility and worse reported everyday shifting and task monitoring. Conclusion. Decreased executive function, namely cognitive flexibility and attentional control, may impair functional cognition in people with PD. Future studies with larger, more diverse samples are warranted to determine the discriminant validity and sensitivity of the CTPA. Use of performance-based assessments such as the CTPA may increase the understanding of functional cognition in people with PD.