Summary: Epilepsy has widespread direct and indirect effects on the patient's quality of life. These patients generally have neuropsychological impairments that lower their educational and occupational levels of achievement, and many have additional emotional and/or behavioral disorders. Multiple factors underlie the cognitive changes associated with epilepsy, including the effect of antiepileptic drug (AED) therapy itself. Although it is recognized that the beneficial results of reduced seizure frequency may compensate at least in part for detrimental cognitive AED side effects, polypharmacy and higher AED blood levels can shift this balance. Further, there is much debate concerning the existence and clinical importance of differential AED cognitive side effects. While all the. major AEDs can produce cognitive side effects, more recent research indicates that the magnitude of these effects may not be clinically significant with monotherapy within standard therapeutic range. The impact of AED differential cognitive side effects on the patient's quality of life is only beginning to be appreciated as research focuses on this important aspect of patient management. The information gained from such investigations will influence not only current therapeutic decisions, but also the development of future anticonvulsants.