Currently there is considerable interest in applying functional imaging modalities to the problem of cortical localization. We present the case of a 15-year-old boy with a seizure disorder related to a tumor in the dominant supplementary motor area. This case illustrates the usefulness of functional magnetic resonance imaging as a new imaging tool for localization of cortical function in younger patients. The functional magnetic resonance imaging provided an anatomically accurate topographic map of operative site and subcortical structures along with relevant functional cortex. This information was useful for both presurgical planning and intraoperative localization. Validation of the technique in this instance was confirmed with intraoperative cortical motor mapping and the postoperative result.