Cognitive impairment is common in children and adolescents with epilepsy. Though there is increasing recognition that even children with more benign epilepsy syndromes may show cognitive loss over time, this is particularly true in children with severe epilepsies, termed the epileptic encephalopathies. The current article discusses general cognition in children with epilepsy, focusing on risk factors for cognitive decline over time in severe epilepsies. The ?epileptic encephalopathies? are briefly introduced and methods for assessing cognitive loss over time are discussed with an emphasis on the use of reliable change indices. The strengths and the limitations of this approach are noted as they pertain to children. The article concludes with an illustrative case example of a young child with a severe epilepsy syndrome and apparent cognitive loss. The utility and limitations of reliable change indices are discussed within the context of this case.