This paper describes the development and use of a simulation model representing part of the medical practice within a Stroke Unit. In particular, we modelled the medical activities as described in a guideline for the ischemic stroke treatment, adopted by the Stroke Unit of our hospital. The Petri net formalism has been chosen for the model representation. The numerical parameters have been estimated both using a database of about 100 patients collected during the last two years, and eliciting knowledge from the neurologists. A commercial tool was used for performing simulations, while ad-hoc routines were written for tailoring the result presentation to the specific context. We consider simulation a very useful preliminary step for the subsequent implementation of a patient workflow (careflow) management system. In fact, simulation is based on the process model (the clinical practice guideline) and on the organisation model (human and technological resources), so allowing to detect bottlenecks in the care delivery organisation and to find the optimal resource allocation. For example, we show that simulation has been able to find some of the causes of the delay in the patients treatment, and accordingly, to suggest changes in the organisation.