The original ACRIN 6664 National CT Colonography Trial included 15 participating sites and a total study data set of 2531 participants. The target study data set for the ACRIN 7151 trial is 520 participants, assigned to one of three cohorts: an E3/E4 Case Group (n = 141) excluding pulmonary nodules, an E3/E4 Pulmonary Nodules Case Group (n = 119), and an E1 Control Group (n = 260) (see Section 8.6). Medical records will be collected by the site from their institutions and from the primary care provider identified by the participant during the ACRIN 6664 trial. Initial record collection will comprise the six months following CTC for all cohorts. Additional medical record collection (from other primary care providers, specialists, and hospitals, and for extended time periods) may be necessary for primary endpoint determination. ECFs are categorized according to the original radiology read of the CTC during the ACRIN 6664 trial.