Abstract-- Objective: To assess the efficacy and safety of the dopamine agonist cabergoline in the treatment of patients with idiopathic restless legs syndrome (CATOR study). Methods: Patients with moderate to severe restless legs syndrome (RLS) were randomly assigned to cabergoline (single evening dose: 2 mg) or placebo and treated for 5 weeks in a double-blind, multicenter polysomnography (PSG) trial. The primary efficacy measures were the periodic leg movements during sleep arousal index (PLMS-AI) and sleep efficiency. These and further PSG variables were monitored by centrally evaluated PSG. Severity of RLS was assessed using the International RLS Study Group Severity Scale (IRLS), the RLS-6 scales, the Sleep Questionnaire Form A (SF-A; quality of sleep), and the Quality of Life for RLS questionnaire. Results: Forty-three patients were treated and 40 patients were evaluated with PSG (age 56 ± 10 years, 73% women). Cabergoline was superior to placebo in terms of the PLMS-AI (-17.7 ± 16.4 vs -4.5 ± 20.0 placebo; p = 0.0024), sleep efficiency (+6.2 ± 13.9% vs +3.3 ± 11.7%; p = 0.0443), PLMS index (p = 0.0014), PLM index (p = 0.0012), and total sleep time (p = 0.0443). Improvements in IRLS total score (-23.7 ± 11.2 vs -7.9 ± 11.0 placebo; p = 0.0002), RLS-6 severity scales during the night (p = 0.0010) and during the day (p = 0.0018), Clinical Global Impressions severity item (p = 0.0003), sleep quality (p = 0.0180), SF-A sleep quality (p = 0.0371), and QoL-RLS (p = 0.0247) were larger in patients treated with cabergoline compared with the placebo group. Adverse events were only mild and well-known side effects of dopamine agonists. Conclusion: Single-evening cabergoline is an efficacious and well-tolerated short-term therapy for sensorimotor symptoms of restless legs syndrome and associated sleep disturbances.