DISEASE CHARACTERISTICS: The following case material must be submitted for each patient: No colonic diseases except polyps, cancer, or diverticulosis Optimal diagnostic computerized tomographic colonography (CTC) data with computed tomography acquisition parameters that meet the following minimal standards: Slice thickness no greater than 5 mm Reconstruction interval no greater than 3 mm Pitch no greater than 2 Anatomic coverage of the entire colorectum Supine and prone data sets Complete colonoscopy performed within 30 days following CTC by a board certified gastroenterologist or a physician with at least 3 years of colonoscopic experience Pathology reports for all endoscopically or surgically removed colorectal lesions with the exception of polyps that are inadvertently dropped at the time of retrieval Photograph or videotape record of dropped lesion allowed as proof of its existence All studies are allowed including those with lesions less than 1 cm, lesions at least 1 cm, or no lesions Report documents size, site, stage, grade, and type of colorectal cancers; size, site, degree of dysplasia, and type of colorectal adenomas; and types of other lesions (e.g., inflammatory, vascular, ulcerative) Demographic data including patient's age, sex, ethnic background, symptoms, risk factors, and relevant clinical history