Background Accurate measures of the total polyp burden in familial adenomatous polyposis (FAP) are lacking. Current assessment tools include polyp quantitation in limited-field photographs and qualitative total colorectal polyp burden by video. Objective To develop global quantitative tools of the FAP colorectal adenoma burden. Design A single-arm, phase II trial. Patients Twenty-seven patients with FAP. Intervention Treatment with celecoxib for 6 months, with before-treatment and after-treatment videos posted to an intranet with an interactive site for scoring. Main Outcome Measurements Global adenoma counts and sizes (grouped into categories: <2 mm, 2-4 mm, and >4 mm) were scored from videos by using a novel Web-based tool. Baseline and end-of-study adenoma burden results were summarized by using 5 models. Correlations between pairs of reviewers were analyzed for each model. Results Interobserver agreement was high for all 5 measures of polyp burden. Measures that used both polyp count and polyp size had better interobserver agreement than measures based only on polyp count. The measure in which polyp counts were weighted according to diameter, calculated as (1) × (no. of polyps <2 mm) + (3) × (no. of polyps 2-4 mm) + (5) × (no. of polyps >4 mm) had the highest interobserver agreement (Pearson r = 0.978 for two gastroenterologists, 0.786 and 0.846 for the surgeon vs each gastroenterologist). Treatment reduced the polyp burden by these measurements in 70% to 89% of patients ( P < .001). Limitations Phase II study. Conclusion This novel, Web-based polyp scoring method provides a convenient and reproducible way to quantify the global colorectal adenoma burden in FAP patients and a framework for developing a clinical staging system for FAP.