This chapter provides an overview of the differences between men and women in terms of brain development, normal cognitive (thinking) skills, and the cognitive difficulties that may result from epilepsy. This chapter emphasizes on the biology of sex differences in brain functioning, but there are many 'nonbiological' factors that also explain differences in behavior between men and women. There are several human disorders that act as 'experiments of nature because they provide information about the cognitive effect of early hormone exposure. Many studies have examined the differences between males and females in the nature and severity of cognitive deficits that develop after brain injury or neurologic disorders. These studies explore whether damage to a specific brain region causes different types of cognitive problems in men and women. Several studies have examined whether men and women differ in their cognitive abilities after epilepsy surgery in the anterior temporal lobe.