This paper presents an empirical examination of firm characteristic determinants of the capital structure of a sample of 299 Irish small and medium sized firms (SMEs). Hypotheses formulated from pecking order and agency theories incorporating a financial growth life cycle approach are tested on a number of multivariate regression models. Results suggest that age, size, level of intangible activity, ownership structure and the provision of collateral are important determinants of the capital structure in SMEs. A generalization of Zellner's (1962) Seemingly Unrelated Regression approach (SUR) is used to examine industry effects and to test the stability of parameter estimates across sectors. Results suggest that the influence of age, size, ownership structure and provision of collateral is similar across industry sectors, indicating the universal effect of information asymmetries. Firms overcome the lack of adequate collateralizable firm assets in two ways; by providing personal assets as collateral for business debt, and by employing additional external equity to finance research and development projects.