Background: Complex movement and balance impairments in people with Parkinson disease (PD) contribute to high fall risk. Comprehensive balance assessment is warranted to identify intrinsic fall risk factors and direct interventions., Objective: The purpose of this study was to examine the psychometric properties of 3 balance measures of a force platform (FP) system in people with PD., Methods: Forty-two community-dwelling individuals with idiopathic PD completed the testing protocol. Test-retest reliability was assessed for the Limits of Stability Test (LOS), Motor Control Test (MCT), and Sensory Organization Test (SOT). Intraclass correlation coefficients (ICC [2,1]) were calculated to determine test-retest reliability and minimal detectable change. Validity was assessed by comparing the FP measures with criterion gait and balance measures using Pearson product moment correlations. Multiple regression analyses examined the contribution of PD characteristics to FP measures., Results: All primary FP variables demonstrated excellent test-retest reliability (ICC=.78-.92). The SOT and LOS demonstrated fair to good correlations with criterion measures, whereas the MCT had fair correlations to balance measures only. Both SOT composite equilibrium and MCT average latency were moderately associated with disease severity., Limitations: This study's sample had a relatively small number of participants with a positive fall history, which may limit the generalizability of the findings., Conclusions: This study's findings provide support that FP measures are reliable and valid tests of balance impairment in people with PD. Disease severity was significantly associated with SOT and MCT measures, perhaps reflecting that these tests are meaningful indicators of decline in postural control with disease progression. Force platform measures may provide valuable quantitative information about underlying balance impairments in people with PD to guide therapeutic interventions for fall risk reduction., (© 2016 American Physical Therapy Association.)