Carbohydrate antigen 19-9 (CA 19-9) is a glycosphingolipid of the Lewis blood group that for years has been proposed as a useful marker for epithelial type gastrointestinal cancers. It is well known that moderately increased concentrations of CA 19-9 can be found in 15-36 % of patients with benign conditions such as pancreatic, liver, biliary diseases and benign hydronephrosis. In current study, we investigated whether there was any tendency for CA 19-9 elevation in 71 patients with Hashimoto's thyroiditis. Patients with malignancy, benign pancreas, liver, lung and biliary diseases, inflammatory bowel diseases, urinary tract infection, hydronephrosis, endometriosis, diabetes mellitus and chronic renal failure were excluded. In the Hashimoto's thyroiditis cases, mean serum CA 19-9 level was 12.5 +/- 10.4 (range, 2.5-55), while it was 11.9 +/- 9 (range, 2.5-29.3) and 10.3 +/- 8 (range, 2.5-28.9) in patients with Graves' and healthy volunteers respectively, without any significant intergroup differences. Although the American Society of Clinical Oncology does not recommend tumor markers like CA 19-9 in screening for malignancies, they may be used for this purpose. In contrast to case reports showing possible elevation of CA 19-9 in Hashimoto's thyroiditis, we did not detect such a relation. Moreover, there was no pointers to change in CA 19-9 levels in patients with hypo-, hyper- or eu-thyroidism.