This article examines whether the assumption of perfect competition in the U.S. dairy industry biases the findings of economic impacts of generic dairy advertising. An imperfect competition model based on an approach similar to that of Appelbaum is developed and used to evaluate generic milk advertising. The results are compared with a perfect competition model. The findings indicate positive price and quantity impacts due to generic advertising. The differences in magnitude of impacts between the two models are small, suggesting that the assumption of perfect competition for U.S. dairy models is plausible.