Forum participants identified challenges involved in applying cost-benefit analysis to the prevention field and discussed how to meet those challenges. They demonstrated how cost-benefit methodology has received new impetus from the likelihood of health care system reform and from the interest in focusing Federal support on cost-effective programs. Forum participants agreed that cost-effectiveness studies of individual programs should build the case for prevention from a record of successful efforts. They characterized the evidence to date for the cost-effectiveness of drug abuse prevention as encouraging but not strong, and they debated whether cost-effectiveness in primary prevention among children and adolescents should be measured by small changes in use rates or by larger changes in risk and protective factors. The forum determined that ethnic/cultural minority communities present special challenges to cost-effectiveness and other evaluation studies related to prevention, that the complexity of prevention efforts poses additional barriers to the application of cost-effectiveness methodology, and that findings from cost-effectiveness studies in the prevention field need to be better publicized and distributed. Suggestions for additional cost-effectiveness studies are offered, and a list of forum participants is appended. 1 table