It was recently suggested that genetic factors could play a major role in the development of Graves' disease (GD). The aim of the present study was to evaluate the frequency of the c.721G-->A polymorphism and the c.1405A-->G polymorphism of the intercellular adhesion molecule 1 (ICAM-1) gene in subjects with GD compared with that in healthy controls, because ICAM-1 was found to play a key role in lymphocyte infiltration into the thyroid gland and the concentration of the soluble form of ICAM-1 correlates significantly with the clinical activity and treatment status in GD. We have analyzed the association of ICAM-1 polymorphisms with the age at onset of GD and the presence of ophthalmopathy. In a group of 235 patients with GD and 211 healthy controls we have shown that polymorphism at position c.721G-->A is associated with an earlier age of GD onset and that the c.1405A-->G polymorphism of the ICAM-1 gene could predispose to Graves' ophthalmopathy. This suggests that G241R and K469E amino acid substitutions in the ICAM-1 molecule could influence the intensity/duration of the autoimmunity process and the infiltration of orbital tissues. It could be speculated that therapy that modulates ICAM-1 function may delay the onset and/or prolong the remission and/or have an influence on clinical manifestations of GD.