The prevalence and clinical correlates of pediatric periodic limb movements of sleep (PLMS) were identified by polysomnography in children attending St Christopher's Hospital for Children, Philadelphia, PA. Of 982 polysomnograms, 77 showed PLMS, a prevalence of 7.8%. Males outnumbered females, 47 to 30. Mean age was 9.4 +/- 4.2 years (range, 1-19 years). Rapid eye movement sleep constituted 16.8% and slow-wave sleep 22% of sleep time. Associated diagnoses included obstructive sleep apnea in 36 (46.8%), ADHD in 10 (13%), migraine in 7 (9.1%), seizures in 7 (9.1%), narcolepsy in 7 (9.1%) and autistic spectrum disorder in 5 (6.5%). Serum ferritin was decreased (mean 26.1 microg) in 29 (96.6%), but the degree of decrease did not correlate with severity of PLMS. Data regarding the efficacy of oral iron in treatment was not available. 
COMMENT. The significance of periodic limb movements of sleep is controversial, some authorities dismissing the movements as a normal variant of arousal patterns, not associated with disturbed sleep and not requiring treatment . Sir Charles Symonds who first described the entity as nocturnal myoclonus affecting 5 adult patients, regarded the movements as a variant of epilepsy . EEGs obtained in 3 patients uncovered bioccipital slowing in one but none showed epileptiform discharges.