This study provides an analysis of 54 operational loss events experienced by eight Australian banks during the period 1990-2007. The results of an event study show that the announcement of operational losses has an adverse effect on the stock price and market value of the announcing bank. Further empirical work reveals no systematic relation between losses and bank characteristics such as size and leverage. The results also show that while the frequency of an event of a certain type is independent from the underlying business line, there is an association between the loss amount and the business line. The decline in market value relative to the loss amount is found to be independent of the type of the underlying loss event.