Using a matched employer-employee data-set, we analyze how workforce diversity in terms of cultural background, education and demographic characteristics affects the productivity of firms in Denmark. Implementing a structural estimation of the firms' production function (Ackerberg et al. 2006), we find that labor diversity in education significantly enhances a firm's value added. Conversely, diversity in ethnicity and demographics induces negative effects on firm productivity. Therefore, the negative effects, which are derived from the communication and integration costs associated with a more culturally and demographically diverse workforce, seem to outweigh the positive effects of creativity and knowledge spillovers.