Spontaneous retroperitoneal hematoma is rare and can cause duodenal obstruction. We report four cases of spontaneous retroperitoneal hematoma with duodenal obstruction, wherein endoscopic ultrasound was useful for diagnosis. The patients complained of vomiting with stable vital signs. Computed tomography, esophagogastroduodenoscopy, and endoscopic ultrasound findings were similar in all cases. Contrast-enhanced computed tomography revealed a low-density mass around the 2nd to 3rd part of the duodenum. Esophagogastroduodenoscopy showed an edematous, reddish, but non-neoplastic duodenal mucosa with stenosis of the lumen. Endoscopic ultrasound revealed a low-echoic mass around the duodenum and high-echoic floating matter suggesting debris and anechoic areas that indicated a liquid component. These findings suggested hematomas or abscesses. Although pseudoaneurysm of the pancreaticoduodenal artery was suspected in Case 3, we chose conservative treatment because the aneurysm was small. In Case 4, median arcuate ligament syndrome was suspected on angiography. No aneurysms or arteriovenous malformations were found; thus, endovascular embolization was not performed. The patients were treated conservatively and discharged within 3–5 weeks. English literature queries on spontaneous retroperitoneal hematoma with duodenal obstruction in MEDLINE revealed 21 cases in 18 studies. The clinical features of these patients and the present four cases have been discussed.