Among the various diseases leading to chronic hyperglycemia, type 1 diabetes mellitus is distinctive by the presence of specific autoantibodies. The common from of type 1 diabetes mellitus is insulin-dependant diabetes, but type 1 diabetes may also present as non-insulin-dependent. In order to predict insulin-dependence and screen for associated autoimmune diseases, search for autoantibodies is required in all patients with diabetes, whatever the clinical presentation. COMPLEX PATHOPHYSIOLOGY: Diabetes mellitus is a multifactorial disease implicating of environmental and genetic factors leading to breakdown immune tolerance. LONG PRECLINICAL PHASE: Chronic hyperglycemia is preceded by a long preclinical phase during which the only observable anomalies result from activation of the immune system. With the development of simplified techniques for detecting autoantibodies, it would be reasonable to foresee large-scale screening. ONGOING SECONDARY PREVENTION TRIALS: The goal is to prevent the development of chronic hyperglycemia by intervening early, during the infraclinical phase, in patients with signs of immune activation. AT THE TIME OF DIAGNOSIS: When diabetes is discovered, intensive insulin therapy helps preserve residual insulin secretion and guarantees better long-term metabolic control.