Drawing on the business case for gender diversity, this article examines whether board gender diversity has a positive effect on firm performance, based on evidence from the Netherlands and Denmark. We use empirical data on 186 listed firms observed in 2007. Almost 40% have at least one woman in the boardroom. Within boards, the average share of women is only 5.4%. To investigate the impact of board gender diversity, two-stage least-squares estimation is applied, using Tobin’s Q as a measure of performance. Our findings indicate that on the basis of this data-set, there is no relation between board diversity and firm performance.