Diabetes mellitus (DM) type I was diagnosed in two children, a girl aged 10.9 years and a boy aged 10.3 years, who suffered from overweight. Both were treated with subcutaneous insulin injections and dietary adjustments. Some of the data in the literature suggest that overweight or obesity during childhood increases the risk of type-I DM. Important in this connection is the so-called 'accelerator hypothesis', which postulates a common basis for both type-I and type-2 DM with genetic predisposition, insulin resistance (caused by rapid weight gain) and autoimmunity, leading to beta-cell insufficiency, as 'accelerators'. It is important to consider a diagnosis of type-I DM in children with overweight or obesity, especially in case of abnormal weight loss associated with polydipsia and polyuria.