OBJECTIVE: We studied ripple-band (80-200 Hz) high-frequency oscillations in scalp electroencephalogram (EEG) in various pediatric epilepsies featuring sleep-activated spikes, such as epileptic encephalopathy with continuous spike-and-wave during sleep (CSWS) and investigated their characteristics. METHODS: The subjects were 94 children with epileptic disorders including idiopathic and non-idiopathic CSWS, benign epilepsy with centrotemporal spikes (BECTS), Panayiotopoulos syndrome, other types of focal epilepsies (oFE), and focal spikes without clinical seizures (Latent). We detected ripple oscillations using a semi-automatic detection tool based on localized power increase. RESULTS: In the idiopathic CSWS Group, the median ratio of ripples per spike in the initial EEG was 5.73, which was significantly higher than those in the BECTS, Panayiotopoulos syndrome, oFE, and Latent Groups (0.39, 0.02, 0.35, 0, respectively, all with p < 0.01). Ripples were particularly frequent at younger ages. CONCLUSIONS: This paper is the first to confirm a high ratio of ripples per spike in CSWS in the largest number of patients to date. SIGNIFICANCE: The dense generation of ripples, which occurs through a combination of heavy loading of individual spikes with ripples and large numbers of spikes during sleep, characterizes CSWS and might be closely related to the pathophysiology of this epileptic encephalopathy.