Although the initial manifestations of narcolepsy in children may differ from those with adult onset, hypersomnia remains the most common presenting sign. This study aimed to (1) describe the clinical and polysomnographic features, and treatment outcomes, of a group of children with narcolepsy, and (2) describe other sleep disorders to be considered in the differential diagnosis of hypersomnia and which may coexist with narcolepsy. A retrospective review of 125 children referred in 1 year for hypersomnia revealed 20 patients (16%) with narcolepsy. Of these, only 15% exhibited cataplexy, 10% experienced hallucinations, and none manifested sleep paralysis. Eighty-five percent of children with narcolepsy had sleep-disordered breathing on polysomnography. Body mass indices of these children were higher than for healthy, age-matched controls subjects. Other polysomnography findings included periodic limb movements of sleep (25%) and parasomnias (5%). The multiple sleep latency test revealed a mean sleep latency of 6.14 minutes, with sleep-onset rapid eye movement periods (median, 2/5 naps). Treatment with modafinil and sodium oxybate provided optimal control of daytime sleepiness. Physicians should routinely screen for hypersomnia in children by obtaining a detailed history and, in appropriate situations, ordering polysomnographic testing to rule out narcolepsy and other causes of hypersomnia.