Several non-neoplastic conditions, i.e., acute and chronic inflammations, benign tumors, renal or hepatic insufficiency, are associated with elevated plasma levels of Carcinoembryonic Antigen (CEA). Usually, CEA elevation in these pathologies is less than 10 ng/ml. CEA values in non-malignant disease can be affected by many factors, which can be classified into five main categories: a) tissular, b) physiological, c) metabolic, d) circulating and e) methodological factors. Synthesis, expression and release are the most important tissular factors. Among the metabolic ones liver, biliary and renal functions play a primary role in the determination of CEA concentrations. In addition, other factors such as the presence of circulating CEA-like substances, autoantibodies and immunocomplexes or the characteristics of the assay method can influence the diagnostic value of the CEA test. All these factors must be carefully considered when the marker is used in clinical practice.