Distinguishing psychogenic nonepileptic seizures (PNES) from epileptic seizures (ES) is a difficult task that is often aided by neuropsychological evaluation. In the present study, signal detection theory (SDT) was used to examine differences between these groups in neuropsychological performance on the Wechsler Memory Scale, Third Edition, Word List Test (WMS-III WLT). The raw WMS-III WLT scores on this task failed to discriminate the two groups; however, with the use of SDT, patients with PNES were found to have a negative response bias and increased memory sensitivity as compared with patients with ES. When patients with left (LTLE) and right (RTLE) temporal lobe epilepsy were compared, the patients with LTLE demonstrated decreased memory sensitivity but a similar response bias as compared with the patients with RTLE. Memory impairment in patients with PNES may be related to faulty decision-making strategies, rather than true memory impairment, whereas memory performance differences between the LTLE and RTLE groups are likely related to actual differences in memory abilities. © 2009 Elsevier Inc. All rights reserved.