Stereotactically implanted depth electrodes are one means of localization of seizure foci. Unilateral seizure focus localization was obtained in 72.7% mesial temporal (MT) implants and 50% of focus/extramesial temporal (MT-XMT) implants. Recent increase in localization to over 80% in MT implants was possible because a larger percentage of patients had MT-XMT implants. Increased localization to 60% in MT-XMT implants was related to using more XMT electrodes per patient and to orienting electrodes to monitor larger limbic XMT and neocortical areas. Since MT foci were localized in 25% of MT-XMT cases, MT electrodes should be included with all MT-XMT implants. Depth electrography can also be used to rule out certain patients as surgical candidates. Therefore, a surgical decision can be reached in a very high percentage of patients undergoing depth implantation. Surgical results are comparable to those in our overall series.