The prevalence and significance of restless legs syndrome was assessed in 307 patients presenting to an acute-care geriatric medical service. Fifteen patients (5%) had restless legs syndrome; 13 (87%) of these patients had insomnia and 10 (67%) reported troublesome or frequent leg symptoms. Of 147 patients with current insomnia, iron deficiency (serum ferritin < 18 ng/ml) was present in 4/13 (31%) patients with restless legs and 8/134 (6%) patients without restless legs (P < 0.025). Improvement in symptoms of restless legs was noted with iron repletion. These findings suggest that restless legs syndrome is relatively common in the elderly and causes significant discomfort and sleep disturbance. Iron deficiency is a common and treatable cause.