A double-blind randomized crossover study of 7.5 mg bromocriptine at bedtime versus placebo was conducted in 30-day phases (with a 2-week washout period between phases) in 6 patients with idiopathic restless legs syndrome. Five patients experienced partial subjective improvement in restlessness and paresthesias on bromocriptine as opposed to placebo and expressed a desire to continue on the medication. On bromocriptine, the patients showed polysomnographically a mean decrease of 43% from control and a mean decrease of 57% from placebo in the number of periodic movements of sleep per hour of sleep (p less than 0.025). Two of 3 patients with abnormally decreased total sleep time and sleep efficiency showed an improvement in these measures on therapy. The dopamine agonist bromocriptine may be a useful therapy in some patients with restless legs syndrome.