The purpose of the present research was to design, implement, and evaluate a schoolbased prevention program in an attempt to prevent problem gambling. The nature and content of the curriculum was derived from existing programs and a careful study of what was known to be effective in other primary prevention programs. The end result was a 5 session program that contained the following elements: 1. Information concerning the nature of gambling and problem gambling. 2. Exercises to make students less susceptible to the cognitive errors often underlying gambling fallacies. 3. Information on the true odds involved in gambling activities and exercises on how to calculate these odds. 4. Teaching and rehearsal of generic decision-making and social problem-solving skills. 5. Teaching and rehearsal of adaptive coping skills. The format of the program was as important as the content. Important elements of the format included: 1. An entertaining and engaging delivery. All lessons were highly interactive and involved group discussions, games, and small group exercises. 2. A strong emphasis on skill learning and application of knowledge. 3. Targeting the social environment of the people receiving the intervention. At one site this was accomplished by placing 'problem gambling' posters around the school and ensuring that all students in grade 10 received the program by the end of the school year. The robust and enduring changes in attitudes toward gambling, knowledge about gambling, and cognitive errors associated with gambling were expected effects of the program. The failure to obtain enduring changes in the ability to calculate gambling odds suggests that this aspect of the program did not receive sufficient emphasis. The changes in gambling behaviour that occurred were not necessarily anticipated, as this program was advocating responsible gambling, not abstinence. Almost all adolescents in the study were gambling at nonproblem levels before the intervention and almost all adolescents continued to be gambling at nonproblem levels after the intervention. The true test of this program's effectiveness concerns its impact on the future incidence of problem gambling among students who received the program compared to students who did not. It is anticipated that the robust and enduring changes in the knowledge, attitudes and errors in thinking achieved in the Experimental group should successfully inoculate many of these adolescents from becoming future problem gamblers. The decreases in gambling behaviour that were obtained should further strengthen this effect. However, a longer term follow-up of these students is necessary to evaluate this hypothesis.