Background and AimsEndoscopic healing is likely to become an important goal for treatment of patients with ulcerative colitis (UC). A simple validated endoscopic index is needed. We validated the previously developed UC Colonoscopic Index of Severity (UCCIS).Methods: In a prospective study, 50 patients with UC were examined by colonoscopy; we analyzed videos of rectum and sigmoid, descending, transverse, and cecum/ascending colon. Eight gastroenterologists blindly rated 4 mucosal lesions (for vascular pattern, granularity, friability, ulceration) and severity of damage to each segment and overall. The global assessment of endoscopic severity (GAES) was based on a 4-point scale and 10-cm visual analogue scale. Correlation of the UCCIS score with clinical indexes (clinical activity index and simple clinical colitis activity index), patient-defined remission, and laboratory measures of disease activity (levels of C-reactive protein, albumin, and hemoglobin and platelet counts) were estimated by using the Pearson (r) or Spearman (rs) method. Results: Interobserver agreement was good to excellent for the 4 mucosal lesions evaluated by endoscopy and the GAES. The UCCIS calculated for our data accounted for 74% (R2= 0.74) and 80% (R2= 0.80) of the variation in the GAES and visual analogue scores, respectively (P <.0001). The UCCIS also correlated with clinical activity index (r = 0.52, P <.001), simple clinical colitis activity index (r = 0.62, P <.0001), and patient-defined remission (r = 0.43, P <.01). The UCCIS also correlated with levels of C-reactive protein (rs= 0.56, P <.001), albumin (r = -0.55, P <.001), and hemoglobin (r = -0.39, P <.01). A rederivation of the equation for the UCCIS by using the data from a previous study combined with those of the current study (n = 101) yielded similar results. Conclusions: The UCCIS is a simple tool that provides reproducible results in endoscopic scoring of patients with UC.