More than 5 million Californians enrolled in HMOs (over 50% of enrollees aged 12-64) are overweight or obese. This policy brief categorizes private HMO enrollees into the seven major health plans operating in California, and provides overweight and obesity prevalence data for each health plan. In addition, the brief also reports the proportion of overweight and obese for each health plan among different age groups and races/ethnicities. Despite controlling for these racial/ethnic differences and age, overweight and obesity proportions still differed among enrollees in the seven major health plans operating in the state. Data for the analysis in this brief came from the 2003 California Health Interview Survey, and the research was funded by the California Office of the Patient Advocate.