Key PointsQuestionWhat are the characteristics of US veterans enrolling or declining participation in the Colonoscopy Versus Fecal Immunochemical Test in Reducing Mortality From Colorectal Cancer (CONFIRM) study?FindingsThis cross-sectional study in 50 126 predominantly male and racially and ethnically diverse veterans at average risk for colorectal cancer found that declining participation in CONFIRM was associated with a preference for stool testing over colonoscopy. This preference increased over the recruitment period and was more frequent in the western US.MeaningThese trends in stool testing preference vs colonoscopy may provide insight into national screening trends in the US.