In two patients with end stage renal failure and not treated diabetes spontaneous hypoglycaemiaes were observed. The lowest levels of glucose in blood serum were: 1.9 mmol/L and 1.16 mmol/L. These levels were accompanied by symptoms of severe neuroglycopenia. Despite of intensive pharmacological treatment recurrent hypoglycaemia episodes appeared for 34 hours in one case and 32 hours in the other. Authors discussed pathophysiological processes leading to hypoglycaemia in end stage renal failure patients. It seems that disturbances in renal gluconeogenesis together with lower degradation of insulin played the key role in creating hypoglycaemia in those two patients.