The aim of this study was to elucidate the relationship between corporate governance, credit ratings and the capital structure of small-to-medium enterprises (SMEs) and large Greek listed firms for the period spanning from 2005 to 2010. Panel regression analysis demonstrates that corporate governance structures and credit ratings play a significant role in the capital structure of Greek listed firms, especially during the crisis period (2008)(2009)(2010). Moreover, firmspecific determinants such as size, profitability, asset structure and growth opportunities are also significant determinants of leverage. Finally, we detect that the influence of corporate governance variables on the capital structure of SMEs is less evident compared with large firms. We attribute this to the active involvement of owners in the management of SMEs, which reduces the need for shareholders to bear the costs of monitoring agents.