Objectives: To describe a novel scoring system for the assessment of tenosynovitis by magnetic resonance imaging (MRI) in patients with rheumatoid arthritis, and assess its intra- and inter-reader reliability in a multireader, longitudinal setting. Methods: Flexor and extensor tenosynovitis were evaluated at the level of the wrist in 10 different anatomical areas, graded semi-quantitatively from grade 0 to 3 (total score 0-30), based on the maximum width of post-contrast enhancement within each anatomical area on axial T1-weighted MR images. Ten sets of baseline and 1-year follow-up MR images of the wrists of patients with rheumatoid arthritis with early and established disease were scored independently by four readers twice on 2 consecutive days. Intra- and inter-reader agreements were evaluated. Results: The intrareader intraclass correlation coefficients (ICCs) were high for status scores (median ICCs 0.84-0.88) and slightly lower for change score (0.74). The smallest detectable difference (SDD) in % of the maximum score was 11.2-11.5% for status scores and 13.3% for change scores. Inter-reader single-measure ICCs were acceptable for both status scores (median 0.73-0.74) and change scores (0.67), while average-measures ICCs were very high for both status and change score (all ≥0.94). The median scoring time per patient (baseline and follow-up images) was 7 min (range 3-10). Conclusions: The introduced tenosynovitis scoring system demonstrates a high degree of multireader reliability, is feasible, and may be used as an adjuvant to the existing OMERACT RAMRIS score, allowing improved quantification of inflammatory soft tissue changes in patients with rheumatoid arthritis.