Lingual microcystic lymphatic malformations (LMLMs) are rare congenital vascular malformations, presenting as clusters of cysts filled with lymph fluid or blood. They are responsible for a heavy burden even with small well-limited lesions because of oozing, bleeding, infections, or even speech, chewing or breathing impairment. Pain and aesthetic prejudice are also frequently reported. The natural history of LMLMs is progressive worsening. LMLMs complex management requires multidisciplinary care in specialised centres, and the wait-and-see approach is frequently used. In complicated lymphatic malformations, whatever the location, treatment with oral sirolimus, an mTOR (mammalian Target of Rapamycin) inhibitor, is often used. Topical sirolimus is a known effective treatment for some cutaneous conditions such as angiofibromas in tuberous sclerosis. Topical applications of sirolimus on the buccal mucosae have been reported in erosive lichen planus and oral pemphigus vulgaris with good tolerance and none to slight detectable blood sirolimus concentrations. The objective of this study is to evaluate the efficacy and safety of a 1mg/mL sirolimus solution applied once daily on mild to moderate lingual microcystic lymphatic malformation in children and adults after 4, 8, 12, 16, 20 and 24 weeks of treatment as compared to usual care (no treatment).