Primary intestinal lymphangiectasia is a rare disorder, characterized by hypoproteinemia due to obstruction of the intestinal lymphatic vessels and loss of lymph fluid in the gastrointestinal tract. The case of a 3-month old patient with protein-losing enteropathy due to a primitive intestinal lymphangiectasia diagnosed with duodenal histology is reported. The adapted formula was replaced by a formula enriched with medium-chain triglycerides (MCT) and the patient presented a clinical and biochemical improvement. The importance of an early diagnosis and the efficacy of treatment with MCT is stressed.