This paper examines the two-way relationship between entrepreneurship and economic performance, using a harmonized data set covering 21 OECD countries in the period 1981-2006. While the relation between entrepreneurship and economic performance has been investigated extensively, most papers in this research field suffer from one or more methodological flaws, so that the important question: "does entrepreneurship cause economic performance?" can still not be answered up till the present day. In this paper we investigate the relationship in a Vector Error Correction Model (VECM) framework. We find evidence for the existence of a long-run equilibrium relation between the level of business ownership and per capita income. We also find evidence that increases in business ownership actually cause economic growth. However, our impulse response analysis reveals that the effect depends on the number of business owners already present in the economy, i.e. we find decreasing marginal returns to entrepreneurship. We also find that the effect depends on the size of the shock (i.e. the increase in entrepreneurship), where too big shocks may lead to negative effects on GDP due to 'overshooting'.