Objective: The aim of this study was to assess the capability of ultrasound shear wave elastography (SWE) in evaluating the muscle stiffness in patients with Parkinson's diseases (PD). Methods: Ultrasound SWE of the longitudinal biceps brachii was performed on 46 patients with PD and 31 healthy controls from May 2013 to October 2013. The stiffness of the biceps brachii muscles measured with quantitative Young's modulus (kPa) was compared between the remarkably symptomatic arms and mildly symptomatic arms in the PD and between PD and controls with unpaired t test. The correlation between the Young's modulus of the biceps brachii measured by SWE and motion scores assessed by unified Parkinson's disease rating scale (UPDRS) part III was analyzed by Pearson's correlation coefficient. The reliability of SWE in assessment of biceps brachii stiffness was tested using intraclass correlation coefficient (ICC). Results: The mean Young's modulus of biceps brachii in remarkably symptomatic arms, mildly symptomatic arms, and healthy controls was 59.94 +/- 20.91 kPa, 47.77 +/- 24.00 kPa, and 24.28 +/- 5.09 kPa, respectively. A significant difference in Young's modulus of biceps brachii was found between healthy controls and all PD patients (all P<.05); however, it was not between remarkably symptomatic and mildly symptomatic arms. A positive linear correlation was found between the Young's modulus of the biceps brachii and the motion score by UPDRS in patients with PD (r= 0.646, P=.000). The ICC for interobserver and intraobserver variation in measuring Young's modulus of the biceps brachii with SWE was 0.74 (95% confidence interval 0.68-0.78) and 0.78 (95% confidence interval 0.75-0.82), respectively. Conclusions: SWE of the biceps brachii can be used as a quantitative assessment of muscle stiffness in the patients with PD. (C) 2016 Elsevier Inc. All rights reserved.