Somatostatinomas are rare neuroendocrine tumors of the gastrointestinal tract that can cause new-onset diabetes. Often the diagnosis is delayed. This case demonstrates this usual delay because the tumor was not considered for over 1 year despite a characteristic presentation. A 42-year-old man presented to his primary care physician with intermittent diarrhea and a 15-kg weight loss over 1 year. During evaluation, he was found to have diabetes mellitus and was treated with oral sulfonylurea. His diarrhea was evaluated with colonoscopy, which was normal. His symptoms persisted over another year, and he presented for a second opinion. A computed tomography scan of the abdomen was done, which showed a 3- to 4-cm mass anterior to the descending portion of the duodenum with marked atrophy of the pancreas. The patient underwent a Whipple procedure, and a 2.6-cm pancreatic endocrine neoplasm was removed, which stained positively for somatostatin, MAK6 (cytokeratin), chromogranin, and Ki-67. Lymph nodes were negative for malignancy. After surgery, his hyperglycemia resolved off all medications and his somatostatin concentration remains normal. New-onset diabetes with diarrhea, weight loss, and abdominal pain, the classic triad of somatostatinoma, should prompt consideration of secondary causes for diabetes, including pancreatic cancer or a somatostatin-producing tumor. Although somatostatinomas are extremely rare, familiarity with the characteristic symptoms, along with the greater availability of reliable radioimmunoassays, should result in an earlier diagnosis of somatostatinoma.