Type 1 diabetes can be diagnosed at any age, but dinical course, genetic, and environmental determinants appear to be heterogenous by age. The common pathway begins with preclinical beta-cell autoimmunity with progressive defect of insulin secretion, followed by onset of hyperglycemia, transient usually partial remission, and finally complete insulinopenia associated with acute and chronic complications and premature death. Current research effort is focused on identification of the genetic and environmental determinants of this process and the ways they interact.