Dairy producers and other dairy industry professionals are generally unaware of the progression or implications of Johne's Disease within a herd. Likewise, they are unfamiliar with the efficacy of various intervention practices. The simulation which we have developed couples a detailed risk assessment tool with a herd prevalence model The resulting simulation allows us to asses or describe a farm situation in six management areas related to Johne's Disease risk: the maternity pen, pre-weaned calves, calves to six months old, breeding age heifers, bred heifers and cows. Next, by describing herd demographics, cattle importation practices and known Johne's Disease prevalence, the simulation produces a projection of prevalence over the next twenty years.; The learner can then select to adopt a test and control plan or to implement intervention practices. By choosing the management area(s) on which they wish to focus and the level of intensity of their interventions, the simulation allows users to projects the course of Johne's Disease prevalence over the ensuing twenty years. Through this exercise, learners come to appreciate the relative effectiveness of various management strategies, the time course necessary for Johne's Disease control and the necessity of adopting a systematic, long range plan for control. This simulation will be one component of a larger computer aided instructional program on Johne's Disease.