Eating disorders (EDs), including anorexia nervosa (AN) and bulimia nervosa (BN), are prevalent disorders that carry substantial economic and social burden. The aim of the current study was to evaluate the modelled population cost-effectiveness of cognitive dissonance (CD), a school-based preventive intervention for EDs, in the Australian health care context.A population-based Markov model was developed to estimate the cost per disability adjusted life-year (DALY) averted by CD relative to no intervention. We modelled the cases of AN and BN that could be prevented over a 10-year time horizon in each study arm and the subsequent reduction in DALYs associated with this. The target population was 15-18 year old secondary school girls with high body-image concerns. This study only considered costs of the health sector providing services and not costs to individuals. Multivariate probabilistic and one-way sensitivity analyses were conducted to test model assumptions.Findings showed that the mean incremental cost-effectiveness ratio at base-case for the intervention was $103,980 per DALY averted with none of the uncertainty iterations falling below the threshold of AUD$50,000 per DALY averted. The evaluation was most sensitive to estimates of participant rates with higher rates associated with more favourable results. The intervention would become cost-effective (84% chance) if the effect of the intervention lasted up to 5 years.As modelled, school-based CD intervention is not a cost-effective preventive intervention for AN and BN. Given the burden of EDs, understanding how to improve participation rates is an important opportunity for future research.