Background. N-Glycolylneuraminic acid (Neu5Gc) is a sialic acid synthesized by animals, but not by humans or birds. However, it can be incorporated in human cells and can trigger immune response. In the present study, we detected anti-Neu5Gc antibodies in samples of the general population and of patients suffering from hypothyroidism/Hashimoto’s disease, which is known to have autoimmune origin.Methods. Antibodies were measured using enzyme-immunosorbent techniques.Results. Serum anti-Neu5Gc IgG antibodies were higher in patients with hypothyroidism (mean: 14.8±15.9 μg/mL, median: 10.0 μg/mL,P=0.0003, Mann-Whitney) and even higher in the group with Hashimoto’s thyroiditis (mean: 31.1±16.3 μg/mL, median: 27.2 μg/mL,P=0.0000, Mann-Whitney) compared to the general population (mean: 5.3±4.7 μg/mL, median : 4 μg/mL). All anti-TPO positive samples had anti-Neu5Gc antibody concentration higher than the mean value of the general population while anti-TPO concentration was increased as anti-Neu5Gc concentration increased. Low concentrations of IgA and IgM antibodies were measured in both general population and patient groups.Conclusion. The increased values of anti-Neu5Gc antibodies in patients with hypothyroidism/Hashimoto’s disease and the correlation of anti-TPO incidence with increased anti-Neu5Gc concentration raise the possibility of an association between anti-Neu5Gc antibody development and autoimmune hypothyroidism.