This study's aims were to determine: (1) prevalence of periodic leg movements (PLMs) in walking prepubertal children consulting a sleep clinic for any sleep disorder; (2) associations between PLMs and other sleep and medical disorders; and (3) the response of other sleep disorders to treatment with the dopamine agonist pramipexol. Clinical evaluation and polysomnography were carried out for a period of 12 months on 252 consecutively seen, prepubertal children with sleep disorders (156 males, 96 females; aged 15mo to 11y, mean 7y 1mo, SD3y 10mo). Sleep disorders unrelated to PLMs were treated, and six children received pramipexol for PLMs. Follow-up included clinical evaluation and polysomnography. Twenty-three per cent of children were diagnosed with PLMs on the basis of polysomnography. The presence of PLMs had usually been unrecognized clinically. The only clinical symptom that could be related to periodic limb movement disorder was a report of leg pains at morning awakening. Only two of 58 children had PLMs without other clinical or polysomnographic findings. Comorbidity seen with PLMs included neuropsychiatric syndromes (n=20), isolated sleep disordered breathing (SDB; n=29), and several other comorbid conditions (n=7). Seven of 11 children seen with attention-deficit-hyperactivity disorder also had PLMs. Surgery for SDB was associated with subsequent cessation of PLMs in 15 of 29 children. Five out of six children with PLMs who received pramipexol were able to tolerate the drug and experienced a complete disappearance of their PLMs. Presence of chronic fatigue, sleepiness, disrupted nocturnal sleep, and difficulties in falling asleep should lead to a systematic search for PLMs that is independent of associated syndromes. Isolated treatment of SDB might help eliminate some, but not all, PLMs.