We examine the determinants of corporate debt maturity while taking into account the interdependent relation between maturity and leverage. We do this by estimating a simultaneous-equations model on debt maturity and leverage for a sample of bond-issuing firms. To compare with previous studies, we also estimate a single-equation model on debt maturity using OLS. We define debt maturity as either the maturity of bonds at issuance (incremental approach), or the percentage of a firm's total debt that matures in more than three years (balance-sheet approach). Corroborating the findings of many previous studies, our single-equation OLS results support the underinvestment hypothesis purporting that firms with greater growth opportunities have shorter-term debt. However, under the simultaneous-equations model, the negative relation between a firm's debt maturity and its growth opportunities ceases to hold. Instead, it is the leverage decision that is influenced by growth opportunities. This suggests that existing models may overestimate the effect of growth opportunities on debt maturity.