A 15-year-old Chinese male with underlying glucose-6-phosphate dehydrogenase deficiency presented with exertional dyspnoea and giddiness. He was not vegetarian and there was no history of bleeding. Physical examination was unremarkable. Full blood count showed microcytic hypochromic anaemia with marked reticulocytosis. A peripheral blood count 2 years previously had been unremarkable. He was found to have iron deficiency anaemia and started on oral iron supplements. Oesophagogastroduodenoscopy and colonoscopy were negative. Despite compliance with iron supplements and administration of intravenous iron, he remained persistently anaemic, requiring regular packed red cell transfusions. Further investigations, including a small bowel follow through, Meckel scan, evaluation for haemolysis and flow cytometric screening for paroxysmal nocturnal haemoglobinuria were all negative. Bone marrow studies showed erythroid hyperplasia with absent iron. A tagged red blood cell scan suggested active intermittent bleeding in the jejunum and proximal ileum. Magnetic resonance imaging of the abdomen showed a sheet-like mass in the mid-retroperitoneum surrounding the coeliac axis, proximal common hepatic and splenic arteries, superior and inferior mesenteric veins and superior mesenteric artery, and abutting the duodenum and proximal jejenum. The patient underwent a laparotomy and was found to have an extensive retroperitoneal lymphangioma extending from the second part of the duodenum to the duodenojejunal flexure. An on-table duodenoscopy showed bleeding lesions in the third part of the duodenum. Because of the high risk involved with a complete resection, only the third part of the duodenum, which had mucosal involvement, was resected. Histology was consistent with a lymphangioma. The patient has been well since, with a normal haemoglobin concentration, red cell indices and iron studies. Lymphangioma is a rare benign cystic tumour occurring mainly in children. It has a variable presentation depending on the site of the tumour, but chronic gastrointestinal blood loss presenting as iron deficiency anaemia is a rare occurrence.