Hypoglycaemia is a frequent finding during the neonatal period and may be due to insulin overproduction. Patients with Beckwith-Wiedemann syndrome have reduced numbers of somatostatin-producing cells and decreased extractable somatostatin. In this study the effect of long-acting somatostatin (SMS201-995) on the glucose and insulin levels in an infant with Beckwith-Wiedemann syndrome and hyperinsulinaemic non-ketotic hypoglycaemia is described. SMS201-995 lowered basal insulin levels while maintaining normal glucose and insulin homeostasis. During fasting however, both glucose levels declined rapidly whereas insulin levels did not. The absence of both ketosis and elevated levels of free fatty acids and lactate during hypoglycaemia, as observed in our patient, are important diagnostic clues since the insulin levels themselves may sometimes be only slightly elevated.