Modern banks are faced with numerous risks in their everyday business. One of the risks in everyday business is the operational risk. Operational risk in accordance with the Second Basel Accord represents the risk of loss stemming from inadequate internal and / or external processes, people, systems or events. There are four core categories of sources of operational risk in banks. It is about: human factor, processes, systems as well as external factors. The importance of operational risk management is also evidenced by the Second Basel Accord which introduces a capital requirement that is directly related to the operational risk assessment. The Capital Requirement of Operational Risk prescribed by the Second Basel Accord is 12%. Other Basel Accords also provide for approaches to calculating capital requirements for operational risk, which banks may use in calculating them. The most sensitive approach to the calculation of capital requirements for operational risk is an advanced approach stemming from internal risk measurement systems and operational losses of banks. In order to be able to use an advanced approach to calculating capital requirements for operational risk, banks must obtain approval from the competent institutions. Some of the banks operating in the Republic of Croatia are using an advanced approach to calculating capital requirements for operational risk. Data on the basis of which capital requirements for operational risk are calculated are provided within the accounting system of the bank, but come from outside. However, banks operating in the Republic of Croatia neglect external sources of operational risk.