Neurophysiological tests have improved the planning of a resection in patients with abnormalities near or involving eloquent cortex. With the use of these neurophysiological techniques, mapping of eloquent cortex in or near a planned resection is possible, allowing the neurosurgeon to optimize the resection, thus improving outcome and lessening morbidity. One type of neurophysiological test, evoked potentials (somatosensory, visual, and brainstem) allows one to identify somatosensory, primary visual or auditory cortex. The most common modalities are the somatosensory evoked potentials (SSEPs), in use for many years. The most frequently used are the median nerve SSEPs, but posterior tibial, ulnar and radial are a few of the other types that can be used. Over the years the techniques have been refined and the usefulness of the test has been demonstrated in both children and adults. With the widespread use of these techniques and with their use in combination with other techniques, what follows will serve as a review of the use of evoked potentials in cortical localization. This review will address the performance, pitfalls and special considerations of using evoked potentials in the operating room for cortical localization.