It is today's general medical opinion that children's diabetes mellitus was uncommon in the past. It was generally admitted at that time the initail stages were so sudden as to make difficut its early diagnosis. It's increased incidence is at present an alarming truth; however, a parallel increase of diabetic coma or of mulminant types has rather dropped. Diabetes may be diagnosed by just considering the main symptoms at the onset which are polydipsia, polyuria and weight loss. If an early diagnosis is not made, acidosis (abdominal pain, nausea, vomiting) may appear within a few days or weeks followed by coma (Kussamul's acidotic respiration and dehydration). Coma may be avoided by an early diagnosis and a life may be saved. It must be stressed that an important percentage of children and adolescents show a slow and gradual evolution (week or months) of their diabetes: gradual weight loss, sometimes with noticeable polyphagia, occasional enuresis, but without other associated symptoms. Asymptomatic, intermittent glucosurias are also frequent; they vary in magnitude an almost always they appear without ketonuria and with fasting normal glycemia. According to our experience they may precede in weeks or months the clinical manifestations of the disease. Postprandial glycemia is a sure diagnostic resource; it is of greater trustworthines than fasting glycemia; therefore we advise it as a routine diagnostic procedure which we recommend widely. In uncertain situations, the oral glucose tolerance test is advisable.