Patients with nonepileptic seizures (NES), those with epileptic seizures (ES), and normal controls were compared on a battery of neuropsychologic tests. Diagnoses were made after intensive electroencephalogram (EEG) monitoring. Excluded from the study were patients with both ES and NES, as well as patients with ES who had evidence of structural brain damage. On all neuropsychologic measures, the two seizure groups were significantly impaired relative to the controls, but there were no significant differences between the ES and NES group performances. Additional neuropsychologic measures were obtained on the two seizure groups but not controls, and again there were no significant differences between the two seizure groups. Further analyses suggested that the NES group's impairment was related to emotional factors. The Minnesota Multiphasic Personality Inventory (MMPI)/MMPI-2 and the Portland Digit Recognition Test were helpful in classifying patients by seizure group. Our results, which are consistent with those of previous studies, suggest that neuropsychologic abnormalities are not pathognomonic of brain dysfunction in this population. However, the Portland Digit Recognition Test (PDRT) and measures of personality are useful for classification purposes in the differential diagnosis of epileptic and nonepileptic seizures.