OBJECTIVE:To develop a magnetic resonance imaging (MRI) atlas for the assessment of osteoarthritis (OA) of the first metatarsophalangeal (MTP) joint, and to assess its intra- and interexaminer reproducibility. METHODS:MRI (proton density with and without fat suppression) was performed on the first MTP joint of 60 participants (30 participants with first MTP joint OA and 30 participants without first MTP joint OA). Characteristic MRI features of OA were then used to develop an MRI atlas of first MTP joint OA. The atlas assessed osteophytes (dorsal metatarsal head, plantar metatarsal head, dorsal proximal phalanx), bone marrow lesions (metatarsal head, proximal phalanx, sesamoids), cysts (metatarsal head, proximal phalanx), effusion-synovitis (dorsal, plantar), joint space narrowing (metatarsal-proximal phalanx, metatarsal sesamoids), and cartilage loss. To assess the reproducibility of the atlas, 2 examiners independently rated the MRIs of 30 participants on 2 occasions. Intra- and interexaminer reproducibility were determined using percentage agreement and Gwet's AC1. RESULTS:Observations using the atlas demonstrated fair-to-perfect intraexaminer reproducibility (percentage agreement from 67% to 100%, and Gwet's AC1 from 0.38 to 1.00) and fair-to-almost-perfect interexaminer reproducibility (percentage agreement from 67% to 98%, and Gwet's AC1 from 0.40 to 0.96). CONCLUSION:An MRI scoring system for the assessment of OA of the first MTP joint has been developed. The atlas demonstrates excellent intra- and interexaminer reproducibility. The atlas has the potential to allow for a better understanding of the cause(s) of pain in first MTP joint OA.