We created the McGill Range of Motion Index (McROMI) to allow us to ascribe a score to global limited range of motion (ROM) in patients with polyarthritis. Our goal was to have an easy-to-use index that required only visual estimation of ROM and could be performed by allied health professionals with limited training. The index was created with a range of motion ranking technique involving rheumatologists at McGill University and its validity was tested in patients with early inflammatory arthritis in the McGill Early Arthritis Registry. We hypothesized a valid index would correlate with various process and outcome measures. We found correlations between the McROMI and function (Health Assessment Questionnaire), Health Related Quality of Life (SF-36), pain, a global assessment of inflammatory disease activity (DAS28), and the number of tender and swollen joints. The McROMI demonstrates good validity as a measure of ROM in early inflammatory arthritis. It will prove useful in future research as a means of controlling for ROM as a confounder of various outcomes and in studies of therapeutic maneuvers to improve ROM.