To investigate the effect of the dopamine D2 and D1 receptor agonist cabergoline on sleep, periodic leg movements (PLMs) in sleep, and early morning motor performance in patients with Parkinson's disease (PD). It was hypothesized that cabergoline had long-lasting beneficial effects on sleep and PLMs in sleep in patients with PD, after a single evening intake. A total of 15 patients with idiopathic PD underwent two nights of polysomnography and motor tests (UPDRS, tapping test) before and after 6-8 weeks of treatment with cabergoline (dosage: 3-6 mg/day). Additionally, patients completed a subjective sleep visual analog scale (VAS) before and during cabergoline treatment. Compared to baseline values, treatment with cabergoline did not change sleep efficiency or the amount of stage 1 and stage 2 sleep. The number of awakenings (22.4+/-10.1 vs 32.5+/-13.3, p<0.05) and stage shifts (119+/-42 vs 148+/-46, p<0.05) were increased during treatment with cabergoline, and PLMs in sleep were reduced (PLM index 34.9+/-44.9 vs 6.7+/-4.2 per hour, p<0.05). Cabergoline significantly improved early morning motor function, and in spite of increased phase shifts and awakenings, patients felt significantly more refreshed in the morning during cabergoline therapy. Cabergoline slightly fragmented sleep, without altering its total amount. The functional significance of this finding is uncertain. The subjective quality of sleep improved, and periodic limb movements in sleep decreased.