The structural abnormality of planum temporale (PT), a part of the superior temporal heteromodal association cortex involved in auditory and language processing, has been implicated in the pathophysiology of schizophrenia. However, its relationship to clinical manifestations remains unclear. Magnetic resonance images were obtained from 17 right-handed Japanese men with schizophrenia and from 22 age-, handedness-, and parental socioeconomic-status-matched healthy Japanese men in order to manually evaluate grey matter volumes of Heschl's gyrus (HG) and PT. Psychiatric symptoms were assessed using positive and negative syndrome scale among the patients. Compared with healthy participants, patients with schizophrenia were associated with a statistically significant PT grey matter volume reduction without left or right lateralization, whereas HG volume was preserved. Smaller right PT volume was significantly correlated with more severe delusional behaviour in the patients. Previous investigations have focused on smaller-than-normal left PT in the pathophysiology of schizophrenia; however, the present results suggest a possible role of the right PT, which is involved in social cognition such as understanding the intentions of others, in the production of psychotic experiences in patients with schizophrenia.