Parkinson disease (PD) is a chronic progressive neurological disorder, often resulting in substantial limitation of function. A number of self-report and performance-based measures have been used to quantify change of disease state or function in people who have PD. These measures have limitations when used to quantify function in individuals in the early or mid-stages of PD, especially in people with preclinical levels of functional difficulty. The purpose of this paper is to (1) review tests and measures currently available to quantify functional limitations of those with PD; (2) determine reliability and concurrent validity of a new measure, the Continuous Scale Physical Functional Performance (CSPFP) test applied to those with PD. Participants were 42 independent, community-dwelling adults with idiopathic PD. Mean (SD) age was 63.7 (11.5); 31.7% were women. Participants completed self-report measures of function, the CS-PFP, and 3 other performance-based tests (Functional Reach, Timed Up & Go, 360° turn). Ten participants were tested twice on the CS-PFP, one week apart. The CS-PFP was found to be a reliable measure of physical function in the early and mid-stages of PD (k = 0.95). The CS-PFP correlated moderately strongly with other self-report measures (eg, United Parkinson Disease Rating Scale (UPDRS) r = -.62, p=.0001; Northwestern University Disability Scale, r = .43, p = .006) and with performance based measures (eg, Functional Reach, r = .70, p = .0001;Timed Up & Go, r = -.69, p = .0001). Multivariate analysis showed the UPDRS to be a predictor of CS-PFP score. The regression model (including control variables of age, sex, depression, and pain) explained over 50% of the variance in CS-PFP; age and UPDRS scores were the significant predictors. The CS-PFP is a reliable and valid measure for determining physical function in individuals who are in the early and mid-stages of PD. This scale identified substantial functional decline to a greater extent than other scales specific to PD.