Many patients with a suspected malignant biliary obstruction are considered unsuitable for surgery because of locally advanced or metastatic disease or poor clinical performance status. Management of these patients is facilitated by a tissue diagnosis at initial endoscopic retrograde cholangio-pancreatography (ERCP). This may obviate further invasive tests, and the most suitable nonsurgical treatment can be initiated without delay. Brush cytology is the most frequently used technique. The procedure is relatively easy to perform, requires little time, and generally is safe. Although its specificity is close to 100%, brush cytology has a modest sensitivity that ranges from 30% to 57% in most published studies .