Objective: To determine the diagnostic accuracy and clinical utility of electromagnetic source imaging (EMSI) in presurgical evaluation of patients with epilepsy. Methods: We prospectively recorded magnetoencephalography (MEG) simultaneously with electroencephalography (EEG) and performed EMSI, comprising electric (ESI), magnetic source imaging (MSI) and analysis of combined MEG-EEG datasets (cEMSI), using two different software packages. As reference standard for irritative zone (IZ) and seizure onset zone (SOZ) we used intracranial recordings and for localization accuracy, outcome one year after operation. Results: We included 141 consecutive patients. EMSI showed localized epileptiform discharges (ED) in 94 patients (67%). Most of the ED-clusters (72%) were identified by both modalities, 15% only by EEG and 14% only by MEG. Agreement was substantial between inverse solutions and moderate between software packages. EMSI provided new information that changed the management plan in 34% of the patients, and these changes were useful in 80%. Depending on the method, EMSI had a concordance of 53-89% with IZ and 35%-73% with SOZ. Localization accuracy of EMSI was between 44% and 57%, which was not significantly different from MRI (49-76%) and PET (54-85%). cEMSI achieved significantly higher odds ratio compared to ESI and MSI. Conclusions: EMSI has accuracy similar to established imaging methods and provides clinically useful, new information in 34% of the patients. Classification of Evidence: This study provides Class IV evidence that EMSI had a concordance of 53-89% and 35%-73% (depending on analysis) for the localization of epilepsy as compared with intracranial recordings - IZ zone and SOZ respectively.