Two entities of special interest in sleep disorders medicine are restless legs syndrome and periodic movements of sleep. Most patients with restless legs syndrome have periodic movements of sleep, but most patients with the nocturnal disorder do not have restless legs when awake. In both conditions, the underlying cause is obscure, and the frequency of occurrence increases with advancing age. In most patients with restless legs syndrome, the results of complete blood cell counts and iron, ferritin, folate, and vitamin B12 levels are normal. No hematologic or chemical abnormalities have been reported in patients with periodic movements of sleep who do not also have restless legs syndrome. Various pharmacologic agents, including benzodiazepines, opiates, and levodopa, have been proposed for the treatment of both disorders. Although some patients respond to a single drug for long periods, in many patients tolerance develops and the efficacy diminishes. In such circumstances, a reasonable approach is to alternate chemically unrelated agents on a weekly or biweekly schedule. Transcutaneous electric nerve stimulation may be beneficial.