Lipid islands in the gastric mucosa are macroscopically well demarcated white or yellow-white patches, microscopically composed of accumulations of lipid-filled macrophages. The occurrence of lipid islands has not previously been linked to gastric surgery. This study presents the prevalence of lipid islands after Billroth I and Billroth II resection as well as in a nonoperated control group. Gastroscopy and multiple biopsies were performed at selected intervals after surgery. The occurrence of single or multiple lipid islands increased with the postoperative time, independent of the original ulcer disease or the type of operation performed. In nonoperated patients, lipid islands were found in 6.3%, and approximately the same prevalence was found 1 to 3 years after gastric surgery. A much higher prevalence was found 10 to 15 years postoperatively, and 23 years after Billroth II resection 60% of the patients demonstrated lipid islands. At repeated gastroscopic examinations over a period of 1 to 2 years, no certain changes in number, size, or distribution of the lipid islands were seen. The etiology of lipid islands is unknown, but intestinal-gastric reflux may be the most plausible etiological factor.