The risks that the banks incur are known as credit and market risks. However in recent years by the occurance of financial crises resulting from the complexity of the developments in the financial products and services; the banking sectors realised the reality of operational risks. Operational risk is basicly defined as all the risks other than credit and market risks. However in recent years the definitions for operational risk is updated. The Basel Committee's definition for operational risk is "the loss resulting from inadequate or failed internal processes, people, systems or from external events". In accordance with the Committee's definition the factors resulting operational risk are grouped in four as human, system, processes and external factors. By the official announcement of Basel II in June 2004, measuring and managing operational risk and including in the banks'capital adequacy computations became one of the most popular subjects in banking sectors. In order to manage operational risks effectively, banks are first recommended to define and classify their operational risk factors. Then it will be possible to measure the effect of each factor and calculate the required capital to minimize the effect of the risk. This paper presents the factors causing operational losses and examines the approaches for calculating capital requirements of operational risk using real data of a bank from Turkish banking sector. Keywords: Operational risk, basic indicator approach, standardised approach, alternative standardised approach, advanced measurement approach.Piyasalarda sunulan ürün ve hizmetlerin gelişmesi ve daha karmaşık hale gelmesiyle ortaya çıkan finansal skandallar sonucu operasyonel riskin bankalar için önemli boyutu anlaşılmaya başlanmıştır. Operasyonel risk genel olarak kredi ve piyasa riski dışında kalan tüm riskler olarak ifade edilmiştir. Basel II düzenlemesinin Haziran 2004 tarihinde yayınlanmasıyla birlikte, bankacılıkta operasyonel risklerin ölçümü ve sermaye yeterliliği oranına dâhil edilmesi konusu daha güncel hale gelmiştir. Bu çalışma, operasyonel riskleri oluşturan faktörleri sınıflandırıp, örnekler yardımıyla açıkladıktan sonra, operasyonel risk için sermaye gereksinimi hesaplama yöntemlerinin bankalar tarafından nasıl uygulanabileceğini sektörde faaliyet gösteren bir bankanın gerçek verilerini kullanarak anlatmaktadır. Anahtar Kelimeler: Operasyonel risk, temel gösterge yaklaşımı, standart yaklaşım, alternatif standart yaklaşım, gelişmiş ölçüm yaklaşımı
