AIM To determine the correlation between clinical, fecal, endoscopic and histologic activity in patients with ulcerative colitis. METHODS A correlational analytic cross-sectional study was performed in patients with ulcerative colitis who underwent colonoscopy between February and December 2016. Clinical, endoscopic, fecal and histologic activities were determined using the Partial Mayo Subscore, Endoscopic Subscore and Mayo Modified Endoscopic Subscore, Fecal Calprotectin and Geboes Score and the presence of basal plasmacytosis, respectively. Scores were analyzed with Spearman's rank correlation coefficient test. To determine the association between scores and some clinical variables and active ulcerative colitis, univariate and multivariate logistic regression were used. RESULTS 105 endoscopic procedures (91 patients), were included. In 65% of the procedures, the mucosa was inflamed; however, 15% did not show histological inflammation. Endoscopic remission was observed in the other 35% of procedures; however, 22% exhibited histologic inflammation in their biopsies. Mayo Endoscopic Subscore and Mayo Modified Endoscopic Score were well correlated but were only moderately correlated with clinical and histologic scores. Further, there was a moderate correlation between Mayo Endoscopic Score and Geboes Score. Conversely, histologic scores were poorly correlated with Partial Mayo Score. Using multivariate analysis, Geboes Score and basal plasmacytosis were predictive of active disease (OR 3.05; 95% CI: 1.54-7.95 and OR 3.24; 95% CI: 1.12-9.34, respectively), whereas biological therapy usage was found to be protective factor for ulcerative colitis (OR 0.02; 95% CI: 0.00-0.64). CONCLUSION Clinical, endoscopic and histologic activities were moderately correlated, while Geboes Score and basal plasmacytosis were predictive of endoscopically active disease.