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The optimal management of oncological conditions is reflected by the careful interpretation of investigations for screening, diagnosis, staging, prognostication and surveillance. Serum tumour markers are examples of commonly requested tests in conjunction with other imaging and endoscopic tests that are used to help clinicians to stratify therapeutic decisions. Serum carbohydrate antigen 19-9 (CA19-9) is a key biomarker for pancreatic cancers. Although this biomarker is considered clinically useful and informative, clinicians are often challenged by the accurate interpretation of elevated serum CA19-9 levels. Recognizing the pitfalls of normal and abnormal serum CA19-9 concentrations will facilitate its appropriate use. In this review, we appraised the biomarker, serum CA19-9, and highlighted the clinical utility and limitations of serum CA19-9 in the investigation and management of pancreatic cancers.