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Summary Objective The study aims at a better definition of continuous spike–waves during sleep (CSWS) with an early thalamic lesion, focusing on various grades of sleep-potentiated epileptiform activity (SPEA). Their possible relationship with different clinical features was studied to try to define prognostic factors of the epileptic disorder, especially relating to behavior/cognitive outcome, in order to improve prevention and treatment strategies. Methods Sixty patients with early thalamic injury were followed since the first registration of SPEA with serial neurological, long term EEG monitoring and neuropsychological examinations, as well as neuroimaging and a detailed clinical history. They were classified in three different groups according to the sleep spike–waves (SW) quantification: electrical status epilepticus during sleep (ESES), more than 85% of slow sleep; overactivation between 50% and 85% and simple activation between 10 and 50%). Results were then examined also with a statistical analysis. Results In our series of CSWS occurring in early brain injured children with unilateral thalamic involvement there is a common neuropathologic origin but with various grades of SPEA severity. Statistical analysis showed that patients evolving toward ESES presented more commonly the involvement of the mediodorsal part of thalamus nuclei and a bilateral cortico-subcortical brain injury, epilepsy was more severe with a delayed onset; moreover, in the acute stage .ESES patients presented the worst behavior/cognitive performances. As to cognitive and behavior outcome, longer SPEA duration as well as bilateral brain injury and cognitive/behavior impairment in acute phase appear linked to a poor outcome; some particular neuropathology (ischemic stroke and haemorrhagic infarction) as well as hydrocephalus shunting are associated with behavior disorders. Conclusions Discrete features seem to support different underlying mechanisms in ESES patients in comparison with less severe SPEA; they represent negative prognostic factors. Longer SPEA duration as well as bilateral brain injury and cognitive/behavior impairment in acute phase seem predictive of a worse cognitive/behavior outcome.