Mucopolysaccharidosis type IIIB is a lysosomal storage disease caused by a deficiency of the N-acetyl-alpha-d-glucosaminidase enzyme involved in the catabolism of heparan sulfate, causing its accumulation in various tissues. We present an 8-year-old patient with mucopolysaccharidosis type IIIB, with a history of chronic diarrhea and endoscopic and histological findings compatible with intestinal lymphangiectasia. After a dietary treatment with a low-fat diet supplemented with mediumchain triglyceride, our patient presents clinical improvement until today. The pathogenesis of chronic diarrhea in patients with mucopolysaccharidosis type IIIB is still unknown. The Linfangiectasia intestinal en un paciente afectado de sindrome de Sanfilippo B Intestinal lymphangiectasia in a patient with Sanfilippo B syndrome presence of intestinal lymphangiectasia in these patients should be investigated, and appropriate dietary treatment should be initiated, if confirmed, to improve their quality of life.