This paper describes the application of Network II.5, a modelling tool, to the development of a model for a Picture Archiving and Communication System (PACS). The model is used to evaluate the performance of a PACS through computer simulation. The work includes interpretation of the ACR-NEMA Standard for Digital Imaging and Communications. This standard adheres to the ISO-OSI reference model which separates the functions of device communication into well-defined layers. In this work, the Application/Presentation, Session, and Transport layers are treated in detail, in fact, the model structure is based on these layers. Results and conclusions show that Network II.5 is useful in this application, however some weaknesses were exposed due to the size and complexity of the final system model.