We report a case of triple cancer of the pancreas, colon, and peripheral nerve sheath. A 68-year-old woman diagnosed with type 2 diabetes at age 63 had been administered antidiabetic oral medications since then. Her HbA1c had been 6.0-7.0 % in NGSP. We found that, in the last 5 months, her HbA1c had increased by 3.5 % and she had lost 9 kg, suggesting the need to check for possibly malignant disease. Contrast-enhanced computed tomography showed 1 tumor each of the pancreas, chest wall. Preoperative colonoscopy showed a tumor of the colon. The first two tumors, diagnosed pathologically as cancer of the pancreas and of the peripheral nerve sheath, were completely resected with no significant metastasis. The third tumor, diagnosed as cancer of the colon, was removed by endoscopic mucosal resection. Symptoms in those with diabetes that include progressive weight loss and deteriorating glycemic control should thus suggest the need to check for possibly malignant disease.