BACKGROUND: Evaluating the use and effectiveness of cancer screening is an important component of cancer control programs. Medicare claims may be a useful source of data when screening older populations, but they are limited in terms of completeness and the ability to distinguish screening tests from those provided for diagnosis or surveillance. RESEARCH DESIGN: A review of the major screening modalities for breast, colorectal, and prostate cancer, Medicare's policies for covering these tests, and the procedure codes used to identify them in Medicare claims. RESULTS: Although Medicare's coverage has been extended to include screening mammography, colonoscopy, sigmoidoscopy, fecal occult blood tests, double-contrast barium enema, and prostate-specific antigen tests, providers have been slow to adopt the corresponding screening codes. CONCLUSION: Challenges persist in measuring screening use, and innovative approaches are required to distinguish screening tests from diagnostic and follow-up evaluations.