Objective: Noninvasive brain imaging tests can potentially supplement or even replace the use of intracranial electroencephalogram (ICEEG), an invasive, costly procedure used in presurgical epilepsy evaluation. This study prospectively examined the agreement between magnetic source imaging (MSI) and ICEEG localization in epilepsy surgery candidates. Methods: Patients completing video monitoring with scalp EEG who had intractable partial epilepsy based on ictal electroclinico-anatomical features were screened. Forty-nine enrolled patients (mean age, 27 years; range, 1-61 years) completed MSI and ICEEG studies. Decisions about ICEEG and surgery were made at a consensus conference where MSI could only influence ICEEG coverage by indicating supplemental coverage to that already planned by an original hypothesis. Results: The positive predictive value of MSI for seizure localization was 82 to 90%, depending on whether computed against ICEEG alone or in combination with surgical outcome. The kappa score of agreement for MSI with ICEEG was 0.2744 (p < 0.01). Interpretation: MSI yields localizing information with a high positive predictive value in epilepsy surgery candidates who typically require ICEEG. This finding suggests that enough clinical validity exists for MSI to potentially replace ICEEG for seizure localization. © 2006 American Neurological Association.