A 53-year-old woman was referred to the outpatient clinic for Internal Medicine, due to an elevated serum concentration of carcinoembryonic antigen (CEA). Hypothyroidism was diagnosed. Following replacement therapy with levothyroxin, the serum concentrations of thyroid stimulating hormone (TSH) and CEA decreased to near-normal levels. No malignancy was found during the remainder of the treatment period. A decreased hepatic clearance of CEA seemed to be the most likely explanation for the observed high CEA concentration in this patient with hypothyroidism. An increased CEA concentration may occur in association with certain malignancies, as well as with non-neoplastic disorders, such as hypothyroidism. As CEA has a low tumour specificity, routine assessment of CEA is not advocated for diagnostic evaluation.