AbstractHealth Maintenance Organizations (HMOs) now serve 15 % of the American population and are a visible part of the competitive health care marketplace in most areas. Shapiro (1) has argued that the recent growth of HMOs may increase the“vigor”of delivery of cancer prevention services to the population because of the organized nature of such practice settings and their historical commitment to prevention. In this report, we will review available evidence about the determinants of effective cancer prevention performance in an effort to assess whether HMOs or various aspects of HMO delivery systems do afford advantages over other methods of delivering cancer prevention services.