Objectives The objective of this study was to examine cognitive and clinical differences among three groups of patients diagnosed with psychogenic nonepileptic seizures (PNESs): those with posttraumatic stress disorder (PTSD), those with a history of trauma but no PTSD, and those without a history of trauma. Methods Seventeen patients who were confirmed to have PTSD based on the Trauma Symptom Inventory-2 (TSI-2) and clinical interview were compared with 29 patients without PTSD who had experienced trauma and 17 patients who denied experiencing trauma. We analyzed demographic data, psychiatric information, trauma characteristics, and neuropsychological variables in these groups. Results Our study revealed that patients with PNESs with comorbid PTSD performed significantly worse on episodic verbal memory (narrative memory); had greater self-reported Total, Verbal, and Visual Memory impairments; and had higher substance abuse history and use of psychopharmacological agents compared with patients without PTSD regardless of a history of trauma. Conclusion The present study showed that patients with PNESs diagnosed with PTSD exhibited memory functions that were significantly different from those in patients with PNESs who do not carry a diagnosis of PTSD (regardless of history of trauma). Furthermore, these specific cognitive findings in narrative memory are consistent with those reported in patients with PTSD alone. The present findings contribute to further identifying discrete intragroup differences within PNESs. Identifying a specific psychopathological subgroup such as PTSD will allow clinicians to accurately select treatment.