Diabetes in childhood is essentially represented by the type 1 or insulin-dependent diabetes mellitus (IDDM). Classical symptoms (polyuria, polydipsia, asthenia, weight loss) are usually present at the first consultation and allow an immediate diagnosis at the physician's office by performing capillary (finger-prick) blood glucose measurement (> or = 200 mg/dL) and urine-stripe test (detection of glucosuria and ketonuria). A diagnosis performed at this stage of the disease leads to the admission of the child at hospital, in order to institute the insulintherapy without delay. This attitude should permit to avoid the rapid development of diabetic keto-acidosis, which is at present too much frequent at diagnosis (50% of the cases) and which is associated with potential risks of severe complications in children. In case of incidental detection of hyperglycemia without ketonuria in childhood, the differential diagnoses of early IDDM are the rare form of familial non insulin-dependent diabetes with onset in childhood (MODY: maturity-onset diabetes of the young) and the transient hyperglycemia in childhood. Finally, diabetes could also develop in the course of an other chronic disease (i.e. cystic fibrosis) or as part of genetical syndroms.