Graves's ophthalmopathy is an extrathyroidal tissue-specific symptom of Graves's disease characterized by inflammatory infiltration of orbital tissues. In several percent of patients the course of disease is severe, leading to serious ocular complications and affecting quality of life. Progress made in understanding the pathogenesis of GO has not been followed by better outcome of treatment and it is still one of the most complex problems of clinical endocrinology. In this respect, qualification for immunosuppressive treatment based on an assessment of the disease activity is a matter of great importance. Glycosaminogycans are linear, unbranched heteropolysaccharides built of repeating disaccharide sequences. These compounds are essential for the organization and function of connective tissue. Moreover, they also take part in the initiation and regulation of immune reactions. In this paper, glycosaminogycans are described with regard to their structure, metabolism, and function, with special emphasis on the tissue specificity of the orbit. Data concerning GAG useful in the management of patients with GO are highlighted.