Oxcarbazepine, the 10-keto analogue of carbamazepine, is approved for the treatment of partial seizures or generalized tonic-clonic seizures. The primary metabolite of oxcarbazepine is monohydroxylated derivative (MHD). This review follows a decision-making algorithm to determine if therapeutic drug monitoring of MHD is warranted.Important factors to take into account include the appropriateness of oxcarbazepine for the therapeutic indication; ability to measure MHD concentrations; existence of a good concentration-response relationship, narrow therapeutic range or unpredictable pharmacokinetic parameters; assessability of the pharmacological response of oxcarbazepine; adequate duration of therapy; and potential influence of MHD concentrations in the clinical decision-making process. Based on the available evidence, therapeutic drug monitoring of MHD is not routinely warranted but may be beneficial in optimizing seizure control at the extremes of age, during pregnancy, in renal insufficiency, or to determine the significance of potential drug interactions or rule out noncompliance.