Primary carcinoma of the duodenum is a rare lesion. In conjunction with the widespread use of panendoscopy, reported cases of carcinoma of the duodenum have recently increased. Although benign hyperplasia of Brunner's gland is well documented, duodenal carcinoma originating in Brunner's gland is extremely rare, and, consequently, there is little data on the morphological or histochemical characteristics. We report here a case of early duodenal carcinoma arising from Brunner's gland, whose origin was proven by mucin immunohistochemistry.