Recently, there has been considerable discussion regarding the classification of drugs as a function of their therapeutic index, defined as the ratio between the upper and lower limits of the therapeutic range. Pharmacologic agents with a therapeutic index < 2 are classified as "narrow therapeutic index" (NTI) drugs. One of the agents classified as an NTI drug is carbamazepine. These recent developments led us to evaluate critically the evidence supporting the classification of carbamazepine as an NTI drug to address an old question: "Does carbamazepine have a narrow therapeutic plasma concentration range?"