A 4-year-old girl was studied at the Pediatrics Unit at the Hospital General de México, S.S.A., with a diagnosis of abdominal tumor, probably malignant. After several laboratory tests (blood count, blood chemistry, catecholamines and the following X-ray studies: chest, skull, long bones, Cava's phlebography and excretory urography), she was submitted to surgery without a diagnosis. After this, the final diagnosis was established: mesenteric panniculitis (mesenteric lipodystrophy. This case is published because of its rare occurrence at this age and because it is important to be kept in mind in the differential diagnosis of abdominal tumors in pediatric practice.