The findings of this study of the effects of health maintenance organizations (HMOs) have implications for consumers' choice between HMOs and other types of insurance: consumers face a trade-off that flows in part from the design of HMOs. HMO enrollees get more primary and preventive care and face lower out-of-pocket costs, bur they get less specialist care, experience more provider access and organizational barriers to care, and report less satisfaction, lower ratings of care, and less trust ill their physicians. Policymakers should recognize that this trade-off will be attractive to some people but not to others.