BACKGROUND: Persistent hyperinsulinaemic hypoglycaemia of infancy (PHHI) is a hyperfunctional disorder of pancreatic insulin-producing cells with hypertrophic beta-cells present either focally or diffusely. With an estimated frequency of 1:50,000 live births, Norway will on average have one case per year. It is clearly difficult to maintain expertise in diagnostics and treatment with such a low incidence. MATERIAL AND METHODS: We report three Norwegian patients with PHHI who were successfully treated at Hôpital des Enfants Malades in Paris. RESULTS: Two patients were shown to have focal hyperinsulinism treated with partial pancreas resection. After follow-up of three and a half and two years respectively, these patients have normal glucose tolerance and exocrine pancreatic function. One patient with diffuse hyperinsulinism was operated with subtotal (90%) pancreatectomy. At 2.5-years follow-up this patient has slight glucose intolerance whereas her fasting blood glucose is low normal. The exocrine pancreatic function is normal. INTERPRETATION: Patients with PHHI should be referred to a centre where the possibility of focal hyperinsulinism can be thoroughly explored.