Three patients with uncontrolled diabetes mellitus and with symptoms due to gastric retention proved to have gastroparesis diabeticorum. The diagnosis was established by the beefsteak-barium meal. After the administration of metoclopramide, gastric emptying improved and the diabetes was easily controlled. Gastroparesis diabeticorum is one cause of uncontrolled diabetes mellitus and may be helped by the administration of metoclopramide.