Drug-resistant epilepsy makes up between 10 and 30% of all epilepsies, and is an important cause of morbidity and mortality. In this article we review the guidelines and techniques used when assessing a patient with drug-resistant epilepsy.Evaluation of a patient with drug-resistant epilepsy requires three steps: first a careful, detailed clinical history to establish the semiological data of the seizure, determine the factors predisposing to drug-resistance (partial epilepsy, history of severe head injury etc.) and to evaluate the antiepileptic treatment given previously and whether the patient actually took the drugs prescribed. Second, a prolonged video-EEG recording is made to determine the type and site of the seizure and decide whether surgical treatment would be suitable. Thirdly, whether structural imaging investigations (magnetic resonance) or functional imaging (sole photon emission computerized tomography or positron emission tomography) should be done. It is also useful to make neuropsychological and psychiatric studies to detect possible associated defects and preexisting psychiatric pathology--which is very common in this population--in order to establish a rehabilitation programme according to the needs of each patient.Careful evaluation of each patient with drug-resistant crises leads to the correct diagnosis of epilepsy with the possibility of its correct classification and localization and may permit improvement or change of the treatment received.