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Background and Aims Mucosal addressin cell adhesion molecule 1 [MAdCAM-1] is upregulated in the vascular endothelium of the colonic mucosa in ulcerative colitis [UC]. Although the association between MAdCAM-1 expression and mucosal inflammation has been discussed, the association with the clinical course of UC patients has not been reported. In this study we investigated not only the association between mucosal MAdCAM-1 expression and mucosal inflammation, but also its association with subsequent relapse in UC patients with clinical remission. Methods Eighty UC patients in remission who visited Kyoto Prefectural University of Medicine for follow-up for 2 years were included. Biopsy samples were collected during colonoscopy, and transcriptional expression levels of UC-related cytokines and MAdCAM-1 were quantified using real-time polymerase chain reaction. MAdCAM-1 mRNA expression and protein expression by immunohistochemistry were compared in patients who subsequently relapsed and those who remained in remission and were examined in relation to endoscopic findings, histological activity and cytokine expression. Results MAdCAM-1 expression was correlated with endoscopic severity, and significantly elevated in histologically active mucosa than inactive mucosa. Furthermore, MAdCAM-1 expression levels were closely correlated with those of several cytokines. MAdCAM-1 mRNA and protein expression were significantly higher in the relapse group than in the remission group, indicating that MAdCAM-1 expression in the mucosa is already elevated in UC patients in clinical remission who subsequently relapse. Conclusions MAdCAM-1 expression in the colonic mucosa of UC patients is related to mucosal inflammation and subsequent relapse; it may serve as a marker for both relapse and therapeutic effectiveness in UC.