Cases of adenocarcinomas developed in Brunner gland hyperplasia (BGH) have been sporadically reported. Herein, we report the morphologic spectrum of hyperplastic changes culminating into dysplasia and carcinoma in 722 cases of BGH listed in our files. Fifteen of these cases showed dysplastic changes, with 8 graded as low-grade dysplasia, 5 as high-grade dysplasia, 11 as atypical hyperplasia, and 2 as invasive carcinoma, although each frequently coexisted in the same tumor. In two carcinomas, one had high-grade dysplasia in the mucosa, and another had only atypical hyperplasia. Interestingly, hyperplastic glands around dysplastic foci were associated with gastric foveolar metaplasia and papillary configuration in 13 cases, 11 of which showed a gradual increase in nuclear atypism in the transition from metaplastic to dysplastic glands. All of the metaplastic gastric glands showed diffuse and strong immunopositivity for gastric foveolar mucin (MUC5AC). Immunohistochemical profiles also supported the concept of a continuous spectrum in carcinogenesis from gastric foveolar hyperplasia through atypical hyperplasia or dysplasia and eventually to frank adenocarcinoma. The results of our study suggest, therefore, that dysplastic and/or carcinomatous change does occur in BGH, that they form the continuous morphologic spectrum, and that papillary foveolar metaplasia may be a precursor lesion in the process of carcinogenesis with a background of BGH.