The authors report the case of a 11-year-old girl admitted for a mesenteric tumor discovered during an appendicectomy. The abdominal Doppler echography and computed tomography (CT) scan showed a 8 x 6 x 7-cm multinodular mass involved in the mesenterium. Biological markers and iodine 131 meta-iodobenzylguanidine (MIBG) scintigraphy results were normal. Percutaneous biopsies were performed. Pathology results showed perilymphatic proliferation of smooth muscle cells leading to cystic lesions. No sign of malignancy was seen. Laparotomy showed a multinodular fixed mass involved from the root of the mesenterium. The superior mesenteric vessels were encircled by the tumor, which could not be resected completely. Partial resection was performed. The pathology and the immunohistochemical tests confirmed the diagnosis of lymphangiomyomatosis. At 21 years of age, she remains asymptomatic. An echography and CT scan showed the mass remaining unchanged in size and echopattern. Lymphangiomyomatosis (LMA) is thought to affect exclusively women in their reproductive life, and the steroid hormones are supposed to play an essential role in the pathology and in the behavior of this condition. Infantile LMA is exceptional. The patient reported is remarkable for her young age, the location of the tumor, her long history, and her benign course. Because the tumor is supposed to be hormone dependent, the surge of oestrogen in this 21-year-old woman may initiate the extensive form of lymphangiomyomatosis with pulmonary involvement, the prognosis of which is extremely poor.