Book excerpt: Introduction: Parkinson’s disease is a common neurodegenerative disorder with clinical manifestations including postural instability, bradykinesia, gait disturbances and strength decline, leading to functional limitations and a high incidence of falls. A clinically feasible outcome measure that is valid, reliable and sensitive for assessing balance and functional mobility in the PD population is needed to add to the current battery of criterion gait and balance measures. The Rapid Step Up test (RST) is a salient functional performance measure with embedded strength and dynamic balance demands. The purpose of this study is to examine the test psychometric properties of the RST in community dwelling individuals with Parkinson’s disease and healthy adults. Methods: Two distinct groups participated in this study: 1) Forty individuals with idiopathic Parkinson’s disease (PD) on stable PD medication regimen (Hoehn & Yahr stage I-IV, mean age= 66.30 (8.07)) and 2) fifty-five age and gender-matched healthy adults (mean age=64.75 (8.50)). All participants passed the screening process and met functional mobility criteria for inclusion in the study. Test-retest reliability was examined by administering the RST twice over a 10-day period. Interrater reliability was examined by having three raters simultaneously time RST performance. Intraclass correlation coefficients for RST were calculated, as well as standard error of measurement and minimal detectable change for both cohorts. Concurrent validity was examined using Pearson correlation coefficients by comparing RST times with criterion gait measures [Functional Gait Assessment(FGA) and MiniBest] and force platform balance impairment measures [Limits of Stability test (LOS), Motor Control Test (MCT), and Sensory Organization Test (SOT)]. Discriminative validity was assessed using Independent t Tests to determine if there was a significant difference in RST between the PD and health groups. Stepwise multiple linear regression analyses examined if there was an association between RST time and age and PD-related variables. An alpha of .05 was utilized in data analysis. Results: A significant difference in RST performance was found between PD and healthy adult cohorts (p