We investigated the clinical characteristics of children with continuous spike waves during slow-wave sleep syndrome and their treatment response to levetiracetam. Five boys and one girl, diagnosed with epilepsy with continuous spike waves during slow-wave sleep syndrome, were enrolled. Their clinical characteristics, including neuroimaging findings, were reviewed. The signs related to continuous spike waves during slow-wave sleep included increased seizure frequency (6/6), impaired responsiveness (3/6), and psychomotor regression (2/6). Magnetic resonance imaging disclosed lissencephaly in one patient, and porencephaly of the left hemisphere in another. The number of antiepileptic drugs before the use of levetiracetam was 0-4 (mean +/- SD, 2.3 +/- 1.5). Five of 6 children demonstrated a good response to levetiracetam, whereas 2 (40%) underwent a relapse of electrical status epilepticus during sleep pattern on electroencephalograms 4 and 5 months after clinical improvement. Both were 5 years old. The most common presenting sign in children with continuous spike waves during slow-wave sleep syndrome is increasing seizure frequency. Levetiracetam is effective in treating children with continuous spike waves during slow-wave sleep syndrome. However, the relapse rate of continuous spike waves during slow-wave sleep syndrome remains high in young children.