Type 1 Diabetes mellitus (insulin-dependent diabetes mellitus, IDDM) is the result of a T-cell mediated destruction of the beta cells in genetically predisposed individuals. Autoantibodies to a variety of islet cell antigens appear during the course of autoimmune insulitis. Type 1 Diabetes is characterized by the presence of distinct circulating autoantibodies including autoantibodies to glutamic acid decarboxylase (GAD), protein tyrosine phosphatase (IA2), insulin, Zinc transport 8 (ZnT8) antibody and autoantibodies directed against cytoplasmic components of islet cells. Measurement of autoantibodies to GAD, IA2, insulin, ZnT8 and of cytoplasmic islet cell antigens (ICA) has been shown to be of significant value for the diagnosis and prediction of type 1 diabetes in first-degree relatives of diabetic patients. ZnT8 antibody complements GAD-65, IA-2, and insulin antibodies as it is positive in 3% to 4% of patients who are negative for GAD-65, IA-2, and insulin antibodies. Use of these 4 antibodies results in 93% to 98% sensitivity. One or several of these autoantibodies are found in most new onset type 1 diabetic patients. They can also be detected before the onset of the disease and characterize the so-called prediabetic period. These autoantibodies help to estimate the risk of an individual developing type 1 diabetes. Testing for all autoantibodies is highly recommended for risk assessment of type 1 diabetes.