Two mediastinal lymphangiomas (KLM) are described, in 36 and 41 year-old women. They presented as an incidental finding on chest radiograph. The mediastinal mass was anterior or posterior, compressing the adjacent vital structures, and cystic on computed tomography. The complete surgical removal was possible, but complicated by the size (12 x 7 x 4 cm and 10 x 7 x 5 cm), the hypervascularization and the infiltrative tendency of the lesions. The patients are well 36 and 30 months after removal. We compare these cases with 109 previously reported. They account for 1 p. 100 of the whole lymphangiomas and for 0.5 to 4.5% of all mediastinal tumours. The congenital or infantile cervico-mediastinal lymphangiomas are more frequent (10%). The general signs, symptoms, pathological findings, treatment and pathogenetic theories are discussed.