Our overall long-term objective is to conduct a large, family-based, genetic-epidemiologic study of colorectal cancer in the region of Galicia, Spain. In the Background section, we describe why we propose a family-based design and why we believe Galicia is an excellent area in which to conduct a family-based study of colorectal cancer. We propose here a two-year pilot study to help us plan the large study that we envision. The specific aims of this pilot study are the following. 1. Collaborate with four hospitals that treat 50 percent of cancer patients in Galicia, to prospectively identify and recruit 10 cases from each hospital. From each case, we will obtain the following items: fresh frozen tissue of the colorectal cancer and surrounding tissue, paraffin-embedded tumor blocks, blood sample, completed risk factor questionnaire, completed food frequency questionnaire, and a pedigree extended to second-degree relatives and cousins. 2. Recruit selected relatives from these families and obtain the following: blood sample, completed risk factor questionnaire, completed food frequency questionnaire, and for cases of colorectal cancer, tumor blocks and pathology reports of their cancer. 3. In the areas served by the four hospitals, attempt to recruit two families from each area with no history of colorectal cancer, to see if our response rates for control families are as high as those for families ascertained through a colorectal cancer case. 4. Estimate from this pilot study the following parameters that will help us plan the larger study: a) response rate of probands for each data item, b) response rate of family members for each data item, c) family history of colorectal and other cancers, d) number of living first- and second-degree relatives and cousins of probands, e) number of these relatives who live in the same household and in the same village, and f) prevalence/distribution of selected risk factors from the risk factor questionnaire and food frequency questionnaire. In addition, by completing this pilot study, we will demonstrate the feasibility of conducting the larger full-scale study.