We aimed to investigate the prevalence of restless legs syndrome (RLS) according to essential diagnostic criteria, and to explore potential associations with clinical features, especially motor fluctuations, in a cohort of 113 patients with idiopathic Parkinson's disease (PD). Twenty-eight (24%) fulfilled essential diagnostic criteria for RLS. They were younger (63.1 +/- 8.6 vs. 68.8 +/- 9.0 years; P = 0.004), had an earlier onset of PD (54.1 +/- 9.5 vs. 59.2 +/- 10.3 years; P = 0.018), and received lower levodopa equivalent doses (578.4 +/- 382.2 vs. 779.1 +/- 459.6 mg/day; P = 0.04) than patients with PD who scored negative for RLS. In 23 patients (82%), RLS symptom onset was after PD onset (mean interval, 4.5 +/- 3.7 years). The majority (n = 17, 61%) who scored positive for RLS reported that the urge to move the legs and unpleasant sensations were associated with wearing off, raising the possibility of RLS mimics in fluctuating patients with PD.