In this cohort, patients with MRI− epilepsies have a lower chance of having surgery than those with lesions demonstrated by presurgical MRI and, if so, less chance of becoming seizure free. This confirms previous data.7,25 The seizure-free outcome rate of MRI− patients who had surgery is, on the other hand, better than that of those who did not. This has not been demonstrated before by direct comparison. The MRI− patients for whom surgery was successful demonstrate that the process of multimodal presurgical evaluation may lead to good outcomes in patients with refractory focal epilepsies, even if they do not have an MRI correlate. When choosing a particular test modality, MRI postprocessing, interictal EEG, and semiology have the highest likelihood of providing inconclusive results. If a certain brain area is contemplated as the to-be-resected area, any conclusive test result may be weighted according to the data given in Table 2. Concordant data from MRI postprocessing, semiology, and ictal surface EEG, in that order, are the best predictors of a seizure-free outcome if the planned resection is done. Discordant results of MRI postprocessing, interictal surface EEG, semiology, and SISCOM are the strongest predictors of a non–seizure-free outcome if the contemplated operation is performed. These predictive values and suggestions have, however, several limitations. They are the results of decisions of the center's clinicians, and the values of these tests may vary depending on the location of the pathology (positron emission tomography, for example, is probably better in identifying mediotemporal lobe than extratemporal foci). Both potential biases can hardly be controlled for in this type of retrospective analysis and small sample size. Epilepsies that are MRI–are not necessarily nonlesional. Thirty percent of MRI− patients in this study and a median proportion of 46% in other series8- 11,13- 17 have epileptogenic lesions. In the present cohort, these MRI− histo+ patients had a postoperative seizure-free outcome as favorable as that of the MRI+ control patients, clearly better than that of the histo− patients who had surgery. Conversely, the proportions of seizure-free patients in the MRI+ and MRI− cohorts who did not have surgery are almost identical, suggesting more similarities than dissimilarities regarding the underlying pathology of the epilepsies. It may be expected that previously MRI− histo+ patients will be found to be MRI+ in the near future, which will increase their chances of proceeding to successful resective epilepsy surgery. Improved MRI acquisition at field strengths of more than 1.5 T and appropriate postprocessing techniques, together with growing experience of MRI evaluators, will likely contribute to this advance.20,26 This assumption is supported by the results of this series; about three-fourths of the false-negative MRIs (ie, those of MRI− histo+ patients) were acquired using 1.5 T systems. Reevaluation by postprocessing and visual reinspection of existing MRI data permitted the detection of underlying brain lesions in all but 1 of 9 such patients. Only 1 temporal lobe FCD IIA remained undetected. Furthermore, the renewed MRI assessment indicated nonresected dysplastic lesions in 2 histo− patients who did not become seizure free after resection of an MRI− histo− area. In both, renewed assessment of presurgical data confirmed that their epileptogenic areas were congruent with the retrospectively identified lesions and had been missed during the original preoperative evaluation. One subsequently had resection after intracranial studies unequivocally confirmed seizure onset in the area, found to be dysplastic during MRI postprocessing.