The Polish breast, ovarian and endometrial cancer study is a complex molecular epidemiologic study that is expected to enroll about 2,500 breast cancer, 450 ovarian and 450 endometrial cancer cases and 2,500 controls from Warsaw and Lodz, two major cities in Poland. This large population-based study combines state-of-the-art techniques of exposure assessment and collection of biological specimens to allow for the study of a wide range of biomarkers. Exposure information is obtained through detailed personal interviews, anthropometric measurements, physical activity monitors, and collection of dust samples from the participants homes. The collection of biological specimens includes blood samples processed as cryopreserved whole blood, serum+ blood clot, plasma+buffy coat+red blood cells; 12-hour overnight urine; paraffin embedded tumor and normal tissue; and fresh tissue from tumors, non-neoplastic breast tissue and mammary fat tissue. Subject enrollment started in June 2000 and is expected to continue until January 2003 for breast cancer cases and controls and June 2003 for ovarian and endometrial cancer cases. As of May 2002, we have identified 2,207 breast, 138 ovarian and 235 endometrial cancer cases and 2,327 controls. The response rates to the interview are 81% for breast, 90% for ovarian and 83% for endometrial cancer cases and 70% for controls. Most women who agree to the interview agree to provide biological specimens (about 90% of cancer cases and controls agree to provide a blood sample), anthropometric measurements (95% of breast cancer cases and controls) and wear a physical activity monitor (79% breast cancer cases and 90% of controls).