The success of AED therapy for epileptic seizures varies according to epilepsy and seizure type. The outcome is excellent in the idiopathic generalized epilepsies, poor in the secondary generalized epilepsies and intermediate for the partial epilepsies. For this latter group, a table of outcome is described in Table I. Overall, approximately 70% of patients can be reasonably managed using one AED, although several may need to be tried before considering monotherapy to be a failure. Of the 30% unsatisfactorily managed by monotherapy, approximately another one-third can be adequately managed given a combination of two drugs. Combinations of more than two drugs provide little if any additional benefit. Evidence that such combinations have efficacy is inferred from the observation of seizure exacerbation when one drug is removed purposely to elicit seizures during evaluation for possible epilepsy surgery. The remaining patients are often considered for trial of an investigational drug although prospects for important improvement are very small even with use of agents shown to be effective and introduced for treatment of epilepsy. Thus, 15% of patients may conservatively be considered for surgical therapy. This would not suggest that all such patients are appropriate candidates from other aspects, but at least they can be considered to have failed all reasonable drug therapy.