Ovarian cancer is the seventh most commonly diagnosed cancer among women in the world and epithelial ovarian cancer is the most predominant pathologic subtype. Tumor markers are widely used in clinical practice to determine therapeutic efficacy, to detect recurrence and to predict prognosis in known cancers. CA-19-9 antigen is mainly elevated in cases of gastrointestinal tract malignancy, including of the pancreas, colorectum, and biliary tract. However, CA 19-9 antigen can also be elevated in ovarian mucinous neoplasms. We report herein the case of a 58-year-old woman who presented with an abnormally high level of CA 19-9 antigen associated with ovarian mucinous borderline tumor.