Effective production systems are necessary for companies to achieve competitiveness in manufacturing, and the production system design process is fundamental to meet this goal. Discrete event simulation is a tool that can support the production system design process. However, few empirical studies have shown the use of this tool prior to the verification of an already chosen alternative, or an implemented production system solution. There is a need to explore how discrete event simulation can be used in the production system design process. A case study at a global manufacturing company, that used this tool in the design of its assembly system, is presented. The results of this study show where and for what purpose were the DES models used for in the production system design process. This study concludes that DES can support this activity and suggestions for future research are made.