Curative services often have been judged by their perceived value, while preventive services have been held to a more rigorous standard of documentation. The dilemma for preventive services is not driven by evidence of their cost-ineffectiveness relative to curative services, but by the paucity of evidence of any type. The issues are whether preventive services of different types are perceived as having value, by what criteria these perceptions are measured, and by whom they are determined. We examine five key constituencies, the measures by which the value of prevention is judged, and the implications for the funding of prevention activities.