We apply signal detection methodology to make predictions about the evolution of Batesian mimicry. Our approach is novel in three ways. First, we applied a deterministic evolutionary modeling system that allows a large number of alternative mimetic morphs to coexist and compete. Second, we considered that there may be natural boundaries to phenotypic expression. Finally, we allowed increasing conspicuousness to impose an increasing detection cost on mimics. In some instances, the model predicts widespread variation in mimetic forms at evolutionary stability. In other situations, rather than a polymorphism the model predicts dimorphisms in which some prey were maximally cryptic and had minimal resemblance to the model, whereas many others were more conspicuous than the model. The biological implications of these results, particularly for our understanding of imperfect mimicry, are discussed.