Purpose – This paper seeks to explore the potential drivers of corporate capital structure. Design/methodology/approach – The paper applies both fixed effects panel models and random effects tobit models to examine this issue. A sample of 379 firms is used across the period from 1991 to 2002. Findings – It is found that corporate characteristics (firm size, firm risk, firm growth rate, firm profitability and asset tangibility) and corporate governance characteristics (board size and outside directorships) are the main drivers of capital structure of UK firms. In addition, the results show that changing the definition of capital structure may result in changing the sign and the significance of these potential drivers. Originality/value – The paper argues that another dimension of the capital structure puzzle can be introduced which is related to the definition of capital structure used in prior studies. It is worth noting that the aim of this paper is not to provide an optimal set of factors that may affect the decision of capital structure, but to highlight the effect of the different definitions of capital structure that can be used by different studies, which makes the comparison between such studies difficult or even erroneous.