The pathogenesis of Brunner gland hamartoma of the duodenum is unknown. This case report describes the chronology of the development of Brunner gland hamartoma from Brunner gland hyperplasia over a 12-year interval. The study subject, a 64-year-old man with chronic iron deficiency anemia, underwent serial upper endoscopies during this period. Repeated endoscopies demonstrated the evolution of Brunner gland hyperplasia, as manifest endoscopically by a submucosal mass, to a pedunculated polyp with histologic features of Brunner gland hamartoma. The duodenal polypoid mass was removed by snare polypectomy. The patient also had a chronic Helicobacter pylori infection of the stomach. This report details the time-dependent evolution of Brunner gland hyperplasia to hamartoma in association with chronic gastric H. pylori infection.