Objectives: (a) To determine test-retest reliability of Game Assisted Rehabilitation System (GRS) for standing balance assessment during Single Task (ST) and Dual Task (DT) conditions in people with Parkinson Disease (PD). (b) To examine the discriminant validity of the GRS to evaluate the potential interaction effect of visuomotor and cognitive loads on standing balance in people with PD. Design: The DT effect of a computer based Game-Assisted Rehabilitation System (GRS) on standing balance activities (DT) was evaluated in 30 individuals with PD (Hoehn and Yahr scale stage 2 and 3). Participants performed a series of game-based visuomotor cognitive tasks and head tracking while standing on sponge surfaces. Testing was conducted on two occasions spaced one week apart. Setting: Data collection and analysis took place in clinical lab of the University. Participants: Thirty participants diagnosed with PD and in stage 2 and stage 3 according to Hoehn and Yahr scale were recruited for the study from the local movement disorders clinic. Main outcome measure: Test-retest reliability was assessed by two-way random model Intra-Class Correlation Coeffi cient (ICC) for sway path length and cognitive outcome measures such as total residual error, response time, movement variation and success rate. Results: Moderate to high test-retest reliability was observed for performance measures of standing balance, visuomotor, and visuospatial executive cognitive functions. A signifi cant DT effect over the majority of standing balance measures and the visuomotor tasks, was observed in individuals with PD. Conclusions: This study demonstrated the reproducibility and validity of the GRS for studying DT interference as well as fall risk assessment in the PD population.