BACKGROUND: 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. AIMS: 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. METHODS: 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. RESULTS: The patient-reported NRS showed excellent correlation with CDAI (R (2) = 0.59, p textless 0.0001), IBDQ (R (2) = 0.66, p textless 0.0001), and HBI (R (2) = 0.32, p textless 0.0001) in patients with CD. The NRS showed poor, but statistically significant correlation with SCCAI (R (2) = 0.25, p textless 0.0001) in patients with UC. The NRS did not correlate with CRP, ESR, or calprotectin. The NRS was reliable and responsive to change. CONCLUSIONS: The NRS is a valid, reliable, and responsive measure that may be useful to evaluate patients with CD and possibly UC.