We prospectively investigated the effects of rate of carbamazepine (CBZ) withdrawal and CBZ level on seizure type and frequency in 12 epilepsy patients withdrawn completely from antiepileptic drugs prior to entering an investigational monotherapy trial. Patients withdrawn from CBZ rapidly (over 4 days) experienced significantly more generalized tonic-clonic seizures (GTCSs) and GTCS clusters than did those withdrawn slowly (over 10 days). Complex partial seizure (CPS) frequency did not differ between the two groups. CPSs preceded GTCSs, with GTCSs occurring in the majority of patients after CBZ had been discontinued, at subtherapeutic or absent CBZ levels. Two of six patients who had been tapered rapidly and all six patients who had been tapered slowly were able to enter the investigational monotherapy trial.