Intellectual deterioration in epilepsy may be real or apparent. The latter refers to delay in cognitive development such that performance against age-related norms appears to drop. The former, real deterioration can occur due to concomitant degenerative neurological disease of which epilepsy is also a symptom, or it may happen as a consequence of one or more of a number of other factors. These include (1) direct effects of seizures and abnormal electroencephalogram activity on brain function, (2) traumatic brain injury secondary to seizures, including status epilepticus, (3) the influence of antiepileptic therapy, both drugs and surgery, on cognitive function, (4) psychosocial sequelae of diagnosis. Some epilepsy syndromes include intellectual deterioration as a frequent feature, with various causes. Developmental factors may also play a part. Cognitive functioning may be impaired by the presence of an epileptogenic lesion, and also in different ways and at different times by other brain areas involved with partial seizures, including irritative and functional deficit zones. Abnormal activity in these areas at critical periods in development may interact and disrupt pathways necessary for maturation of frontal lobe and limbic system functioning, leading to long-term neurological deficits. Increased understanding of the mechanisms by which this may happen raises intriguing possibilities for prevention and remediation.