While the estimation of the degree of market power is a widely discussed topic in the economic literature, the interaction between imperfectly competitive markets and agricultural policy modelling has been seldom considered in simulation models. This study empirically addresses this issue with an application to the Italian dairy sector. First, a model of imperfect competition is estimated using a multi-output framework drawn from a direct demand system. Then, results are used in a policy simulation model where the restricted hypothesis of perfect competition is used as a benchmark. Results show a significant degree of market power for some products that has a substantial implication on the projected policy scenario.