From 12 Patients surgically explored because of suspected insulinoma, the diagnosis was correct in 11. In 8 patients there was a solitary insulinoma, which was diagnosed in every case by preoperative ultrasonography, computed tomography or angiography. In one patient with three adenomas, only one was diagnosed preoperatively, the second by palpation and the third by intraoperative sonography. One patient had a diffuse hyperplasia. The intraoperative frozen section was correct in 9 from 11 patients. The preoperative localisation of insulinoma assisted in the intraoperative identification. The intraoperative pancreatico sonography is an useful help in localisation of insulinoma. For treatment the enucleation of tumor is preferable.