Type 1 diabetes mellitus is a disease caused by the autoimmune destruction of insulin-producing pancreatic beta-cells that takes place in genetically prodisposed individuals. Autoantibodies and autoreactive T lymphocytes reacting with islet target molecules or protein of glycolipid nature have been shown in the circulation of individuals and of animal models of type 1 diabetes (NOD mouse and BB rat) before and at the onset of the disease. As far as autoantigens of glycolipid nature is concerned, gangliosides such as GT3, GD3 and especially GM-1, have been shown to be target of autoantibodies associated to autoimmune diabetes. Of particular interest is the islet-specific monosialo-ganglioside GM2-1, which is target of an autoimmune response highly associated to future progression to diabetes development in first degree relatives of type 1 diabetic individuals. This molecule is recognized by IgG autoantibodies which have been detected before the appearance if clinical diabetes both in man and in the NOD mouse, representing a novel marker of beta-cell autoimmunity.