The purpose of this research is to examine whether U.S. banks that announced material operational risk loss (oprisk loss) events can still enjoy a lower cost of capital. I use the bank's credit rating as a proxy for the cost of debt capital, and the actual oprisk loss amounts announced by publicly traded U.S. banks for $10 million and over during the period 1998 to 2012 compiled from my own database. I also investigate whether the type of oprisk loss event and business line in which the loss event was incurred matter to credit rating agencies. I perform additional analysis to determine whether a downgrade in a bank's credit rating associated with the announcement of a material oprisk loss amount impacts the bank's reputation. This study focuses on the U.S. banking industry because of the increased market and regulatory scrutiny of oprisk losses; especially during the financial crisis of 2008 to 2010. The logistic analysis shows that banks' announcement of material oprisk loss amount is associated with a decline in credit ratings. The findings did not support the position that the type of loss event and business line in which the loss event was incurred matter to credit rating agencies. The results for the event study show that a downgrade in a bank's credit rating associated with an announcement of a material loss amount has a robust, statistically significant negative stock market reaction. Furthermore, the results reveal that the losses in market value significantly exceed the announced loss amounts associated with credit rating downgrades, indicating reputational loss to the banks. This research was limited to announcements of material oprisk loss amounts by U.S. banks publicly traded on major U.S. stock exchanges. Investigating the impact of announcements of material oprisk loss amounts by financial institutions publicly listed on major stock exchanges worldwide provides an avenue for future research. This study contributes to the literature on operational risk and the cost of debt capital as reflected in credit ratings by providing empirical evidence of the impact of oprisk losses on credit ratings of U.S. banks.