We aimed to investigate and compare sonographic abnormalities in the substantia nigra (SN) in patients with idiopathic restless legs syndrome (iRLS), those with RLS and Parkinson's disease (RLS-PD), those with idiopathic Parkinson's disease (iPD), and healthy controls. Study participants totaled 60 patients with RLS (41 iRLS, 19 RLS-PD), 25 iPD patients, and 35 age-matched healthy controls. Comparing all groups, the SN region's echogenicity area in the iRLS patients was significantly decreased compared with that in the PD-RLS, iPD, and control groups (p < 0.0001), and the PD-RLS group demonstrated a significantly increased echogenicity area compared with the control group (p < 0.05) and iRLS group (p < 0.0001). We found that the RLS-PD group's sonological results and clinical findings were different from those of the iRLS group. Copyright © 2010 Elsevier Ltd. All rights reserved.