Cerebral limbic structures modulate the endocrine function of the hypothalamopituitary axis in both animals and humans. In an investigation of 30 women who had complex partial seizures with unilateral temporal lobe epileptiform discharges and reproductive endocrine disorders, there was a significant difference between the EEG laterality distributions associated with polycystic ovarian syndrome (PCO) and those associated with hypogonadotropic hypogonadism (HH). There was a strong predominance of left-sided discharges (15 versus one) with PCO, and right-sided discharges (12 versus two) with HH. Each distribution differed significantly from that of 30 women with epilepsy who had no reproductive endocrine disorder (left/right: 17/13). Moreover, among women with PCO who had unilateral non-temporal lobe foci, six of seven had right-sided epileptiform discharges. This represents a significant difference from the EEG laterality distribution among women with PCO who had temporal foci. These relationships between altered patterns of reproductive hormonal secretion and the predominant laterality of EEG epileptiform discharges in women with epilepsy are consistent with a lateralized asymmetry in cerebral influences on reproductive endocrine function.