Patients with the clinical diagnosis of hypoglycemia secondary to a putative insulin secreting pancreatic neuroendocrine tumor require accurate localization of the tumor and definitive surgical resection. Non-invasive pre-operative imaging studies such as CT, MRI and ultrasound often fail to accurately localize the lesion prior to surgery. Invasive imaging such as arteriogram and selective arterial stimulation are a major improvement, but may not be needed in all patients. This trial will evaluate the ability of laparoscopic exploration with intraoperative ultrasound to localize the insulinoma and allow for its resection with a single procedure.