The authors report a new case of leiomyosarcoma of the duodenum. The exoluminal growth and the volume of this tumor explain the difficulties of the imaging methods diagnostic. Computed tomography, magnetic resonance imaging and angiography were not sufficient to determine the origin of the tumor. Surgical exposure itself was not conclusive and only pathology provided the definitive diagnosis. We think that endoscopic ultrasonography should be indicated in these submucosal tumors of the duodenum to differentiate them from pancreatic neoplasms.