Background & aims - Because transmural healing (TH) could be the best therapeutic target in Crohn's disease (CD), we aimed to build and validate a score to assess TH and transmural response (TR), and to confirm their association with favorable CD outcomes. Methods - DEVISE-CD project encompassed 2 retrospective cohorts (274 and 224 patients with CD for development and validation phase, retrospectively) and 1 multicenter prospective validation cohort (N = 46 patients). A step-by-step process was used to build the modified Clermont score (C-score). The primary end points were time to bowel damage progression, and steroid-free clinical remission with fecal calprotectin <250 at 1 year for retrospective and prospective validation cohorts, respectively. Results - Edema, ulcer, contrast enhancement, diffusion-weighted hyperintensity, fat wrapping, bowel thickening (>3 mm), and enlarged lymph nodes were associated to higher risk of bowel damage progression (P < .01). Edema, diffusion-weighted hyperintensity, post-gadolinium contrast enhancement, and bowel thickening were highly coexistent (>95%) and collinear (P < .0001). Bowel thickness had the highest sensitivity to change after treatment (standardized mean difference = 0.30 ± 1.0; P = .001). C-score was calculated as 0.2x(bowel thickness-3mm) + 1.5x enlarged lymph nodes + 2x ulcer. TH (C-score <0.5; hazard ratio [HR], 0.28 [0.13-0.63]; P = .002; adjusted HR [aHR], 0.15 [0.04-0.53]; P = .003), TR50 (50% decrease of C-score; HR, 0.30 [0.15-0.63]; P = .001; aHR, 0.36 [0.14-0.88]; P = .025), or TR25 (25% decrease of C-score; HR, 0.37 [0.19-0.71]; P = .003; aHR, 0.46 [0.23-0.94]; P = .034) prevented bowel damage progression in development and validation cohorts, respectively. In the prospective validation cohort, achieving TH (OR, 4.6 [1.3-15.6]; P = .016), TR50 (OR, 6.9 [1.8-26.0]; P = .008), or TR25 (OR, 6.0 [1.6-22.3]; P = .008) after 12 weeks of anti-tumor necrosis factor therapy led to higher rate of corticosteroid-free remission at 1 year. Conclusions - C-score is a validated, reliable, and easy-to-use tool to assess TH and TR in patients with CD.