Objective      To detect gray matter structural changes in drug-naive patients with obsessive compulsive disorder (OCD)

and investigate the correlations between abnormal gray matter volume and clinical symptoms.       Methods      Twenty-one OCD patients and 21 normal controls (matched with age

sex and education level) underwent magnetic resonance imaging (MRI). The imaging data were analyzed with a voxel-based morphometry method. The Yale-Brown obsessive-compulsive scale (Y-BOCS)

Hamilton depression rating scale (HAMD) and Hamilton anxiety rating scale (HAMA) were used to assess clinical symptoms.       Results      Compared with the normal controls

the OCD patients showed regional gray matter atrophy mainly in the bilateral orbitofrontal cortex

anterior cingulate cortex

right thalamus and right cerebellum (P0.05

FDR corrected). The gray matter volume in the left orbitofrontal cortex of the OCD patients showed a negative correlation with the total scores of Y-BOCS (r=-0.63

P0.01).       Conclusion      The structural abnormality of the cortical-striatal-thalamic-cortical loop plays a vital role in the pathogenesis of OCD. In addition

the abnormality of cerebellum and other structures may also be involved in the pathophysiology of OCD.