This study investigated the extent to which the Consumer Assessments of Health Plans Survey (CAHPS) distinguishes performance of Medicare managed care (MMC) health plans. Results indicate that CAHPS ratings and report composites distinguish among plans both nationally and within markets. Global ratings of a health plan and reports on customer services varied strongly at the individual plan level, with smaller effects seen at regional and Metropolitan Statistical Area (MSA) levels. Ratings of doctors and health care, and reports on experiences in the doctor's office varied more among regions and among MSAs than among plans within the same MSA. These patterns are consonant with our hypotheses about the determinants of these ratings: customer service is a distinct plan function, but medical services are provided by networks that often overlap for plans in the same area. We conclude that the CAHPS-MMC survey can inform consumers choosing among plans as well as policymakers and researchers.