ABSTRACT: Current instruments used to measure disease activity and health-related quality of life in patients with Crohn's disease (CD) and ulcerative colitis (UC) are often cumbersome, time-consuming, and expensive; although used in clinical trials, they are not convenient for clinical practice. A numeric rating scale (NRS) is a quick, inexpensive, and convenient patient-reported outcome that can capture the patient's overall perception of health.The aim of this study was to assess the validity, reliability, and responsiveness of an NRS and evaluate its use in clinical practice in patients with CD and UC.We prospectively evaluated patient-reported NRS scores and measured correlations between NRS and a range of severity measures, including physician-reported NRS, Crohn's disease activity index (CDAI), Harvey-Bradshaw index (HBI), inflammatory bowel disease questionnaire (IBDQ), and C-reactive protein (CRP) in patients with CD. Subsequently, we evaluated the correlation between the NRS and standard measures of health status (HBI or simple colitis clinical activity index [SCCAI]) and laboratory tests (sedimentation rate [ESR], CRP, and fecal calprotectin) in patients with CD and UC.The patient-reported NRS showed excellent correlation with CDAI (R (2) = 0.59, p < 0.0001), IBDQ (R (2) = 0.66, p < 0.0001), and HBI (R (2) = 0.32, p < 0.0001) in patients with CD. The NRS showed poor, but statistically significant correlation with SCCAI (R (2) = 0.25, p < 0.0001) in patients with UC. The NRS did not correlate with CRP, ESR, or calprotectin. The NRS was reliable and responsive to change.The NRS is a valid, reliable, and responsive measure that may be useful to evaluate patients with CD and possibly UC.