The case of a 17-year-old woman is described, in whom a suspected diagnosis of primary intestinal lymphangiectasia was confirmed endoscopically and histologically only after a high-fat meal had been given the night before the procedure. A characteristic endoscopic finding was the appearance of tiny white dots scattered in the duodenum and jejunum, which on histological examination proved to be dilated lymph vessels. Treatment with low-fat diet and MCT-supplementation was successful.