Achieving endoscopic remission (Mayo endoscopic score of 1 or 0) appears to be the optimal clinical target in ulcerative colitis, reducing risk of relapse, hospitalizations, complications, and need for surgery. While attaining complete endoscopic remission (MES 0) appears to reduce these risks further over mild endoscopic activity (MES 1), the etiologic factors for why MES 0 might be the superior target is poorly understood. Given the putative role of the gut microbiome in driving underlying endoscopic activity and subsequent relapse risk, we sought to define the microbial landscape of UC among patients who achieve either MES 0 vs MES 1 endoscopic remission, especially since the colonic microbial constituents of UC in remission remain uncharacterized.