PURPOSE: To determine the reliability of carpal angle measurement using sagittal wrist MR images for thediagnosis of dorsal intercalated segmental instability (DISI) or ventral intercalated segmental instability(VISI). MATERIALS AND METHODS: In ten asymptomatic adult volunteers, capitolunate, scapholunate, and radiolunate angleswere measured on lateral radiographs and five different series of sagittal MR images, and compared andstatistically analysed. The four MR series, obained in a prone position, with the wrists over the head, were asfollows : A, sagittal images parallel to the third metacarpal bone axis, in a neutral position ; B, obliquesagittal images parallel to the fourthe metacarpal axis, in a neutral position, ; C and D, sagittal imagesparallel to the third metacarpal bone axis, with the wrist at 15degree radially and ulnarly deviated positions,respectively. The fifth true sagittal MR image (E) was obtained in a supine position with the wrists locatedbeside the trunk, in a neutral position. RESULTS: In the MR series performed in the prone position, thecapitolunate and radiolunate angles measured in the series A, B and D were significantly larger than those seen onlateral radiographs. The scapholunate angle showed a statistically significant difference(p=.014) in series D,where one case showed DISI configuration at a scapholunate angle of 81degree. In other series, the angles were notsignificantly different from those seen on lateral radiographs. CONCLUSION: The lunate appears more dorsallytilted on sagittal MR images obtained in the prone position with the wrists above the head than on lateralradiographs, and a DISI configuration can be minicked. IF diagnosing wrist segmental instability by interpretingsagittal MR images without lateral radiographs, there is potential risk of misdiagnosis. It is believed that wristpositioning is crucial for the correct measurement of angles.