Objective: To investigate cognitive workload during a visual search task in patients with Parkinson's disease (PD). Background: Visual search is one of the most important features of human activity. Visual search may be impaired in PD, which in turn may negatively affect daily life activities, such as driving. While previous studies explored visual exploration strategies during visual search tasks, no study investigated cognitive workload during visual search in PD. Cognitive workload refers to the total amount of mental effort being used to perform a task. Methods: Twenty patients with PD (age: 69 ± 8 yo; sex (Men/Women): 16/4) and 15 controls (age: 61 ± 11 yo; sex: 8/7) performed a visual search task on a driving simulator, that provides a context similar to visual search during real-life driving. They were instructed to search for a target road sign among distractor road signs. In half of the trials, the target was present (target-present trials). Response times as well as measures of cognitive workload for correct detections trials were investigated in the two groups. Cognitive workload was measured by the Index of Cognitive Activity (ICA), which was based on the number of times per second that an abrupt discontinuity in the pupil signal was detected. To investigate the cognitive workload over time for correct detection trials in the two groups, response time values were transformed to a continuous scale of percentage completion time, ranging from 0 (start of the trial) to 100% (button press) since response times were different between participants. Results: PD patients were significantly slower than controls to respond correctly to the visual search task, particularly for target-present trials. PD patients had increased values in cognitive workload throughout the entire duration of the task when compared to baseline (p < 0.05). By contrast, few significant differences were observed in controls (at 5% and 15%). Conclusions: These findings suggest that PD patients required increased and longer effort to correctly perform the visual search task compared with baseline cognitive workload. The use of ICA in patients with PD while performing a static visual search task provides new information into the effort (cognitive workload) required by patients on a moment-to-moment basis.