Thirteen patients are described who, on routine endoscopy of the upper gastrointestinal (GI) tract, were found to show a characteristic appearance in the proximal duodenum. This consisted of multiple small mucosal nodules, predominantly in the anterior wall. All cases were biopsied, and showed identical histological appearances of heterotopic gastric mucosa of body type. The incidence of this condition is probably much higher than reported previously, and may be present in up to 2% of the population. In all our patients a diagnosis was reached, other than heterotopic gastric mucosa, to explain the GI tract symptoms. In none was a healed or active duodenal ulcer evident and in none was there a history of a pre-existing ulcer. In our opinion these nodules are probably of little or no clinical significance.