This article addresses the relationship between cameral structure and policy performance in the member states of the OECD for the time period from 1971 to 1996. The empirical analysis shows that bicameral structures act as a significant brake on government intervention and on the expansion of the welfare state. Furthermore, bicameralism is a powerful veto player to block reforms in economic and financial policy. With the exception of the over-representation of small and sparsely populated areas, none of the advantages that classical political theory ascribes to second chambers has actually been confirmed. Bicameral structures pose no barrier to executive dominance, nor do they promote stability within political systems or improve the quality of democracy or economic performance. On the contrary, with regard to social representation, they have a strong negative effect: in comparison to systems with a single chamber, bicameralism significantly reduces women's electoral success.