Nesidioblastosis is characterized by hyperfunction of pancreatic islets caused by hypertrophic beta cells. Postprandial symptoms of hypoglycemia are the clinical presentation of the disease. A female patient with diabetes mellitus who underwent a Roux-en-Y gastric bypass began to present postprandial symptoms of hypoglycemia. There was no radiologic (MRI) evidence of insulinoma. Selective arterial calcium-stimulation test identified hyperfunction only in the splenic artery. Laparoscopic spleen-preserving distal pancreatectomy was performed. The patient has been entirely free of any postprandial symptoms for 10 months after the partial pancreatectomy.