A 65-year-old man was admitted to our hospital with gastrointestinal bleeding. Seventeen years previously, he had a Billroth II procedure for a bleeding duodenal ulcer. A gastroscopy performed on admission showed a stomal ulcer with signs of recent haemorrhage. In the proximal end of the afferent loop, we saw retained gastric mucosa. Histological evaluation confirmed the existence of antrum gastric mucosa. Other diagnostic test for retained gastric antrum were normal. The different approaches in the diagnosis of retained gastric antrum, the importance of our findings and the clinic implications are discussed. We conclude that endoscopic management may be the first diagnostic method in the assessment of retained gastric antrum, and it's possible to find gastric mucosa in the proximal end of the afferent loop (antrum retained), without clinic manifestations.