The key-profile model (originally proposed by Krumhansl and Schmuckler, and modified by Temperley) has proven to be a highly successful approach to key-finding. It appears that the key-profile model can be reinterpreted, with a few small modifications, as a Bayesian probabilistic model. This move sheds interesting light on a number of issues, including the psychological motivation for the key-profile model, other aspects of musical cognition such as metrical analysis, and issues such as ambiguity and expectation.