In a randomized, controlled and double-blind cross-over trial with L-Dopa and placebo we evaluated the effects of a single bedtime dose of L-Dopa 100 to 200 mg on sleep quality and frequency of periodic leg movements (PLM) in 17 patients with idiopathic and in 11 patients with uremic restless legs syndrome (RLS) by polysomnography, actigraphy, and subjective ratings. Treatment with L-Dopa showed significant reduction of the number of periodic leg movements and the PLM-index most pronounced during the first 4 hours of bedtime. Subjective evaluation confirmed improvement of sleep quality. L-Dopa proved to be effective in idiopathic and uremic RLS without any severe side effects.