Studies show high comorbidity between post-traumatic stress disorder and psychotic symptoms. Despite this fact, there has been only one published study of the neurobiology of this enigmatic disorder. This preliminary study examines the relationship between psychotic symptoms in post-traumatic stress disorder (PTSD) and schizophrenia by measuring smooth pursuit eye movement (SPEM) in subjects with PTSD and secondary psychotic symptoms, schizophrenia, and healthy controls. The results show that PTSD with secondary psychotic symptoms is associated with a SPEM deficit that is different from the SPEM deficit associated with schizophrenia.