The CONCeRN Trial is a multi-center study of asymptomatic women between the ages of 40 and 75 referred to regional military medical centers for routine colorectal screening. The primary purpose of the main study is to determine the extent to which advanced neoplastic lesions will be missed if clinicians only perform sigmoidoscopies rather than full colonoscopies as a screening procedure and to resolve current debate about the significance of sigmoidoscopic detection of single, small, tubular adenomas (i.e., do they imply greater risk for large adenomatous polyps or colorectal cancer at other sites beyond the reach of the sigmoidoscope, or is there no increased risk?). Women enrolled in the trial receive colonoscopy during which all identified polyps are removed and also during which two pinch biopsies of apparently-normal tissue are taken. In addition, before the colonoscopy is performed, patients will have blood drawn and answer a brief questionnaire on risk factors for colorectal cancer. The NCI-led sub-study added a more extensive questionnaire to assess dietary and other lifestyle factors potentially related to colorectal cancer, and obtained additional blood for assessment of nutritional status and for analysis of genetic polymorphisms related to colorectal cancer. With the additional information available from these questionnaires and blood samples, it will be possible to explore the extent to which various dietary and genetic risk factors are related to colorectal polyps in asymptomatic women of average risk for disease. Recruitment is now complete at all sites. A total of 937 women were recruited. Of these, about one-quarter of the women with one or more adenomas had an advanced adenoma, defined as being greater than or equal to 1 cm in diameter, or having high grade dysplasia or villous elements). These neoplasia prevalence figures are in line with initial projections. Active contact with participants is concluded. We have now entered into a data analysis phase.