The CA 19-9 antigen is a marker whose concentration is elevated usually in the presence of gastrointestinal cancer. CA 19-9 is considered to be characteristic for pancreatic and biliary cancer; however, an elevated level of this marker may also indicate a cancer with a different point of origin such as the colon or the stomach. CA 19-9 has limited application in diagnosis; however, the observation of its level makes it possible to monitor treatment progress and can help in the detection of cancer spread. CA 19-9 is a glycoprotein with a molecular mass of 210 kD, produced not only by cancer cells, but also by gastrointestinal and liver cells during foetal development, by salivary glands, mature pancreatic and biliary cells as well as the bronchi. This study presents the cases of patients who were diagnosed with significantly elevated CA 19-9 levels and in whom cancer was excluded in the course of further clinical follow-up. The authors indicate that a very high concentration of CA 19-9 can have a different cause than cancer: in the cases described in the present study it was usually cholestasis caused by benign biliary diseases that led to the elevation of this marker.