This paper describes a simulation-based technique for the performance prediction of message- passing applications on cluster systems. Given data measuring the performance of a target cluster in the form of standard benchmark results, along with the details of the chosen computing configuration (e.g., the number of nodes), it is possible to build and to validate automatically a detailed simulation model. This makes it possible to predict the performance of fully-developed or skeletal code off-line, i.e., without resorting to the real hardware. The reasonable accuracy obtained makes this approach particularly useful for preliminary performance testing of parallel code on non-available hardware. After a description of the approach and of the construction and validation of the simulation model, the paper presents a case study.