Auditory P300 abnormalities in schizophrenia patients have been repeatedly reported by many studies. However, reported relationships among P300 abnormalities, clinical features and other biological variables, such as abnormalities in structural brain imaging, are notably discrepant. This is partially due to the inclusion of patients who have had long-term administration of neuroleptics and those from whom this treatment has been withdrawn. The present study measures event-related potentials in 13 neuroleptic-naive schizophrenia patients using an auditory oddball paradigm to clarify the relationships among P300 amplitude, clinical features and brain structure. All patients underwent computed tomography to estimate the area of the right and left frontal cortical sulci and Sylvian fissures. Clinical symptoms were assessed using the Positive And Negative Syndrome Scale. The high correlation coefficients were obtained between P300 amplitude and the anxiety/depression factor score (r = -0.77), the positive factor score (r = -0.58) and between P300 amplitude and the area ratios of the fronto-temporal region (r = -0.66). These findings show that fronto-temporal region and P300 amplitude are closely related to the earliest stage of illness even in neuroleptic-naive patients.