Fourteen patients, aged from 5 to 14 years, with syndrome of electrical status epilepticus during slow sleep (ESESS) have been studied. The absence of epileptic attacks was observed in 21.5% of patients and diagnosis was established by a combination of continuous diffuse epileptiform activity with marked cognitive disturbances. In 78.5% patients, epileptic attacks presented as follows: pharyngeal and oral, hemicephalgia (100% patients with attacks), hemiclonic (18%), atypical absences (27%), negative myoclonus (18%), automotor (18%), focal adverse with vomiting (18%), secondary generalized (36%). Drugs of choice were valproate (depakine) and topamax in patients with attacks; suxilep and frisium in the absence of attacks and in case of continuous diffuse epileptiform activity on the sleep EEG. Two variants have been singled out by the character of ESESS syndrome. The first one, a "symptom variant", was featured by mostly hemiclonic, secondary generalized and automotor epileptic attacks, presence of continuous regional or lateral, less frequent diffuse epileptiform activity, detected by the local structural lesions in MRI, marked cognitive disturbances persisting after stopping of the attacks. The second ("idiopathic") variant is characterized by normal development of children before attack manifestation, appearance of mostly "rolandic" attacks, atypical absences and negative myoclonus, presence of exclusively continuous diffuse epileptiform activity in the phase of slow sleep, standard MRI results (moderate cortical subatrophy in single cases), cessation or substantial decrease of cognitive disturbances after attack stopping. It is emphasized that prognosis of ESESS syndrome should be considered separately with regard to attacks and cognitive disturbances. A prognosis for attacks is always favorable. Cognitive disturbances despite the therapy can persist for a long time.