Objective Temporomandibular joint (TMJ) arthritis in children with juvenile idiopathic arthritis (JIA) is extremely common but frequently asymptomatic. Magnetic resonance imaging (MRI) with contrast remains the gold standard for identifying TMJ arthritis in JIA. A reliable scoring system with published MRI examples of typical acute and chronic TMJ arthritis changes will be invaluable for future prospective treatment trials of TMJ arthritis in JIA. Methods MRIs were collected from routine clinical studies assessing TMJ arthritis in JIA. Representative images were selected for publication to depict acute (synovial fluid, bone marrow edema, and synovial enhancement) and chronic (pannus, disc derangement, and condylar head flattening and erosions) TMJ arthritis findings. A preliminary MRI-based scoring system for assessing degrees of acute and chronic TMJ arthritis was developed and tested for inter- and intrareader reliability. Results TMJ MRIs representative of acute and chronic TMJ arthritis in JIA were selected from among thousands taken (>500 TMJ MRI studies annually at Children's of Alabama) since September 2007. Moreover, computed tomography scans depicting select bony changes (osteophyte formation, micrognathia) were chosen for publication. A description of the MRI protocol for assessing TMJ arthritis is included. A preliminary scoring system weighted for degree of acute and chronic TMJ arthritis MRI findings was found to have substantial inter- and intrareader reliability. Conclusion A published set of MRIs depicting representative acute and chronic changes will help establish a standardized scoring system to assess TMJ arthritis in children with JIA. Future validation will aid in assessing improvement during treatment trials of TMJ arthritis. Copyright © 2014 by the American College of Rheumatology.