In this chapter, we evaluate the behavior of fuzzy estimations of demand for releasing manufacturing orders in a Vendor-Managed Inventory (VMI) supply chain, which is based on a collaborative deal between retailer and manufacturer, and focuses on the interchange of information about demand and inventory levels. The supply chain considered consists of an end consumer, a retailer and a manufacturer. A system dynamics model with fuzzy estimations of demand has been constructed for supply chain simulation. Fuzzy numbers are used to model fuzzy estimations of demand. With a numerical example, we show that the bullwhip effect can be effectively reduced at the level where fuzzy orders exist and that the fill rate reached improves at the retailer level.