Objective: To evaluate the MRI fi ndings in different status of anti-aquaporin 4 (AQP4) antibody in Thai patients with idiopathic infl ammatory demyelinating CNS diseases (IIDCDs). Methods: A retrospective study of 135 IIDCDs patients was performed. The available brain and spinal MRI were reviewed. All were tested for anti-AQP4 antibody. The MRI fi ndings were analyzed for any difference between patients with seronegative and seropositive anti-AQP4 antibody. Results: Eighty cases included 47 seronegative and 33 seropositive anti-AQP4 antibody were reviewed. Forty seven brain and 20 spinal MRIs from the seronegative group and 32 brain MRIs and 27 spinal MRIs (one with only spinal MRI) from the seropositive group were analyzed. There was no signifi cant difference between the two groups upon the number of patients who fulfi lled Barkhof’s MRI Criteria. When the patients were classifi ed according to the location and pattern of abnormal MRI fi ndings, more cases in the seropositive group had lesions at corticospinal tract or subependymal third/fourth ventricles (p<0.05). Long-extensive spinal cord lesion and central gray matter location were found more in the seropositive group whereas the short segment, peripheral location were found more in the seronegative group (p<0.05). Most of the seropositive cases had lesions at the cervicothoracic level in contrast to the seronegative cases which had more lesions at the thoracic cord level. Conclusion: MRI features were different between IIDCDs patients with seronegative and seropositive anti-AQP4 antibody. The characteristics and locations of the MRI lesions were mo