The insula is increasingly the subject of great interest in psychiatric disorders of neurodevelopmental origin because of its anatomical location, wide interconnectivity, and variety of functions. This study explores the possible morphometric change of the insula in schizophrenia and obsessive-compulsive disorder (OCD), and its potential relationship to clinical symptoms. The insula was traced on all coronal slices of magnetic resonance images of three age- and sex-matched diagnostic groups, which consisted of 21 patients with schizophrenia, 21 patients with OCD and 21 normal volunteers. The volumetric measures of the insula were compared among the three groups, and their relationships to the symptom severity were investigated. Volumetric reduction of the left insula was observed in the schizophrenia group, but not in the OCD group. These results confirm the involvement of deficient insular function in the pathophysiology of schizophrenia.