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Background: In order to clarify the clinical significance of P300 as a biologic marker that can reflect schizophrenic symptomatology, many previous studies have evaluated the relationship of P300 with the symptoms on the basis of a positive/negative dichotomy, but yielded inconsistent conclusions. Such a dichotomy has been criticized as being too reductionistic. Recently, most studies with factor-analytic procedures have extracted some symptom factors outside this dichotomy. Therefore, it is important to examine associations of P300 with the symptom factors extracted by these statistical analyses., Methods: In the present study, the amplitudes of P300 were measured by using an auditory oddball paradigm for 73 schizophrenics whose psychopathology was assessed with the Positive and Negative Syndrome Scale (PANSS)., Results: The principal component analysis of the PANSS items revealed five factors labeled the thought disorder, negative, hostile/excitable, delusional/hallucinatory, and depressive factors. The score for the thought disorder factor correlated negatively with the amplitude of P300 recorded at Pz T5, and T6, but that for the other factors did not., Conclusions: These findings suggest that the reduction of P300 amplitudes recorded at the midline parietal and bilateral temporoparietal regions may be one of the electrophysiologic indices representing the thought disorder clinically observed in schizophrenia.