This work aims to determine the existence and relative importance of knowledge spillovers through labor mobility from multinational companies (MNCs) that operate under the free zone regime in Costa Rica. For it, 41,149 former MNCs employees were identified between the years 2001 and 2007, inclusive. It was also determined how many of these employees created their own companies in Costa Rica after they left the MNCs and how many moved to work at local companies. The results show that there were a total of 1,735 start ups. Of these new companies 83.3% (1,445) still continued operating in the year 2010, which implies a very low rate of mortality. In addition, according to the owners of these companies (original founders) their yields in sales and assets are equal or superior to the average of their competitors. It was also explored the impact of the knowledge spillovers on the performance of local companies that have hired former MNCs employees. In so doing, we try to measure such an impact on sales, employment and productivity. Using some econometric models it was found evidence that these companies obtain a much better performance in terms of the growth of their sales and employment than companies that do not hire former MNCs employees. However, it was not found such evidence when the performance of the local companies was analyzed in terms of the average labor productivity.