Due to its unique bicompartmental anatomy and spatial configuration, the sacroiliac joint can be more accurately defined by computed tomography (CT) than conventional radiography. Using a tilted gantry and paraaxial scanning technique, the synovial portion of the joint is oriented vertically on the CT image, while the ligamentous portion is oriented oblique-horizontally. The tilted CT gantry technique allows full ventral-dorsal imaging of the synovial portion of the sacroiliac joint. We have found the accuracy of CT to be superior to conventional radiography in the detection of early erosive sacroiliitis and joint space narrowing. In all patients with discrepancy between the two radiologic techniques, the changes were either only demonstrated or better demonstrated by CT than conventional radiography.