The present study explores the frequency of RLS in PD and focuses on the clinical differences between patients with and without restless legs syndrome (RLS). A cross-sectional study was designed, comprising 114 patients diagnosed with PD. Those patients positive for RLS were assessed for intensity of the syndrome (IRLS). We compared the clinical characteristics of the patients with and without RLS, using specific scales: Unified Parkinson's Disease Rating Scale (UPDRS I-IV), quality of life (Parkinson's Disease Questionnaire, PDQ 39), sleep symptoms (Parkinson's Disease Sleep Scale, PDSS), and diurnal hypersomnia (Epworth Sleepiness Scale). Twenty-five patients (21.9%) out of a total of 114 subjects diagnosed with PD met the RLS diagnostic criteria. RLS was more frequent in women (68%). The patients with RLS showed poorer scores on the PDSS (PD-RLS+: 102.4 +/- 15.1 vs PD-RLS-: 113.2 +/- 16.4) (P = 0.005) and in the bodily discomfort dimension of the PDQ-39 (PD-RLS+ 6.1 +/- 3.4 vs PD-RLS- 3.8 +/- 2.6) (P = 0.002). Analysis of the subscales of the PDSS showed significant differences (P < 0.001) between both groups of patients in items 4 and 10, and to a lesser degree in items 5 (P = 0.01) and 11 (P = 0.02) There was no increased incidence of diurnal hypersomnia in the group of patients with RLS. There were no differences in the rest of the variables. RLS is frequent in patients with PD, though this condition doesn't apparently affect quality of life or lead to an increased presence of diurnal hypersomnia. It would be advisable to validate the diagnostic criteria of RLS in this specific group of patients.