Krenn synovitis Score has been developed by Krenn et al. in order to assess synovitis severity and is used in synovial research. Cell signature of synovial tissue can be studied using immunohistochemistry and is of interest as a biomarker for both prognosis and prediction of response to treatment. However, no synovitis score including immunohistochemistry exists yet. In order to answer this unmet need, we propose a new Immunologic Synovitis score (IMSYC) adding 5 components to the Krenn score: CD68, CD3, CD20, CD31 and Ki67 immunostaining. In this study, we aimed to validate this new IMSYC by studying its diagnostic performances in a well-defined collection of synovial samples. Synovial samples from patients were obtained during surgical procedures. CD68, CD3, CD20, CD31 and KI67 immunohistochemistry were performed. In total, 77 patients were included. In total, 45 were females, mean age was 63.1 years. Forty had inflammatory arthritis, mainly rheumatoid arthritis (31/40). Non inflammatory arthritis group included 35 patients with mainly osteoarthritis. Mean Krenn score and IMSYC were significantly higher in the inflammatory group (P<0.001). ROC analysis of diagnostic performances determined the score of 13.5 out of 24 as the cut-off that gave the best ratio for discrimination between inflammatory and non-inflammatory arthritis with a sensitivity of 71.8% and specificity of 98%. We propose a new synovitis score including immunohistochemistry. This score has a better sensitivity and specificity than the Krenn score and represents a more functional synovitis evaluation. IMSYC could be further used in better categorizing synovial tissue phenotype and give a basis for tissue driven therapy. Copyright © 2018 Société française de rhumatologie. Published by Elsevier Masson SAS. All rights reserved.