We have been interested in demonstrating the usefulness of the reverse endoscopic cholangiopancreatography, a technique already accepted in extrahepatic biliary pathology and the cholangiocarcinoma diagnosis. First of all we reviewed those cases diagnosed as cholangiocarcinoma using the REC and we found that only in 14 (60.9%) of a total of 23 cases the diagnosis was confirmed by surgery, resulting in a false positive ratio of 39.1%. In the second analysis of 22 patients who underwent surgery and whose surgical diagnosis was cholangiocarcinoma, we confirmed a correct presurgery diagnosis by REC in 14 (63.6%) with a false negative ratio of 36.3% which could be reduced to 26.3% after excluding the technically incorrect explorations or those in which only the pancreatic ductus was visualized. We conclude that cholangiocarcinoma diagnosis by REC has a high false positive or negative ratio, thus, treatment, specially non surgical, of a possibly malignant stenosis or obstruction of the bile duct can not only be based on choleangiopatic findings.