Abstract: This paper investigates the relationship between firm efficiency and leverage. We consider both the effect of leverage on firm performance as well as the reverse causality relationship. In particular, we address the following questions: Does higher leverage lead to better firm performance? Does efficiency exert a significant effect on leverage over and above that of traditional financial measures of capital structure? Is the effect of efficiency on leverage similar across different capital structures? What is the signalling role of efficiency to creditors or investors? Using a sample of 12,240 New Zealand firms we find evidence supporting the theoretical predictions of the Jensen and Meckling (1976) agency cost model. Efficiency measured as the distance from the industry's ‘best practice’ production frontier is positively related to leverage over the entire range of observed data. The frontier is constructed using the non-parametric Data Envelopment Analysis (DEA) method. Using quantile regression analysis we show that the reverse causality effect of efficiency on leverage is positive at low to mid-leverage levels and negative at high leverage ratios. Firm size also has a non-monotonic effect on leverage: negative at low debt ratios and positive at mid to high debt ratios. The effect of tangibles and profitability on leverage is positive while intangibles and other assets are negatively related to leverage.