Opaque ventilated façade systems are increasingly used in buildings, even though their effects on the overall thermal performance of buildings have not yet been fully understood. The research reported in this presentation focuses on the modeling of such systems with EnergyPlus. Ventilated façade systems are modeled in EnergyPlus with module "Exterior Naturally Vented Cavity." Not all façade systems can be modeled with this module; this research defined the types of systems that can be modeled, and the limitations of such simulation. The performance of a ventilated façade system, designed and built in Italy, was monitored to analyze its performance and compare on-site measurements to results from simulation. The comparison showed that in this case the EnergyPlus module can be used to realistically predict envelope thermal behavior. Problems are encountered when the façade system includes a ”massive baffle” (i.e. when baffle material is heavy and has high heat capacity) or a composite baffle.