Brunner's gland adenomas are rare, benign, duodenal tumors that occur in middle age. These lesions are often discovered accidentally during upper gastrointestinal (UGI) endoscopy or can sometimes manifest as UGI bleeding or duodenal obstruction. The definite diagnosis is determined by histology. We report a case of Brunner's gland adenoma presenting with UGI bleeding and epigastralgia. UGI endoscopy revealed a giant polypoid mass about 4–5 cm in diameter with a central shallow ulcer in the duodenal bulb. Endoscopic ultrasonography (EUS) revealed a mixed echoic, pedunculated mass arising from the submucosa or mucosa with an intact muscle layer and several cystic lesions within the mass. The patient underwent surgical excision of the tumor and recovered without sequelae. We suggest that the multiple cystic changes in a heterogeneous mixed echoic mass are the key EUS features of Brunner's gland adenoma. EUS plays an important role in the diagnosis of Brunner's gland adenoma before histologic confirmation of the resected tumor.