Most commercial loans are made on a secured basis, yet little is known about the relationship between collateral and credit risk. Several theoretical studies find that when borrowers have private information about risk, the lowest-risk borrowers tend to pledge collateral. In contrast, conventional wisdom holds that when risk is observable, the highest-risk borrowers tend to pledge collateral. An additional issue is whether secured loans (as opposed to secured borrowers) tend to be safer or riskier than unsecured loans. Empirical evidence presented here strongly suggests that collateral is most often associated with riskier borrowers, riskier loans and riskier banks. © 1990.