Abstract: This study examines the relation between bank relations and market performance in Thailand, an economy in which commercial banks play a crucial role through lending relationship and, for a number of companies, equity ownership. Overall, bank relationships, both equity-based and debt-based, positively affect capital investment. However, there is a negative relation between lending relationships, both short-term and long-term, and market performance indicating that bank lending may not always be consistent with value maximization. There is also evidence of a positive marginal effect of bank monitoring through equity ownership on market performance. Further, the relation between bank equity ownership and market performance appears to be non-linear with a concave function. Ownership by corporate insiders is also negatively related to bank equity ownership. Overall, the findings highlight the detrimental effects of excessive short-term debt usage, one of the factors believed to contribute to the financial crisis in Thailand, and the marginal benefit of the equity-based relationship on firm value.