The findings of upper gastrointestinal series (UGI), computed tomography (CT), and sonography (US) of ten duodenal adenocarcinoma confirmed by surgery (n=7) and endoscopic biopsy (n=3) were retrospectively analyzed. We performed US in all cases, CT and UGI in 8 out of 10 cases. UGI showed 4 cases of ulcerating type, 3 of stenotic type, and one failed to visualize duodenum due to previous gastrojejunostomy, UGI was more accurate in depicting the mucosal changes such as ulcer, however, it played a limited role in the evaluation of extraluminal extension. US showed 4 cases of hypoechoic wall thickening. 3 of hypoechoic extraluminal mass, and one of polypoid intraluminal mass but 2 were not detected on US, US accurately detected hepatic and pancreatic metastasis, however, it played a limited role in the evaluation of direct colonic invasion. CT showed was eccentric wall thickening in 4 cases, large extraluminal mass in 2, and low density intraluminal mass in one but one was missed on CT.CT was the most accurate modality to determine the extent of the lesion and adjacent or distant metastasis but it could be misdiagnosed as submucosal tumor if the extraluminal component is large. UGI, CT and US and be used complementary for accurate diagnosis of a duodenal cancer. US may be used as a screenin g tool for detecting duodenal cancer.