Sirolimus, by targeting the mammalian target of rapamycin (mTOR) pathway, has demonstrated efficacy on lymphatic malformations (LMs) in adults and neonates. The current hypothesis is that the earlier the lesion is treated, the better it responds. This has prompted the idea that sirolimus administration might be efficacious to treat fetal LMs as well. Here we report a successful management of a cervicofacial fetal LM with sirolimus taken orally by the mother from the 22nd week of pregnancy until 2 weeks before planned delivery. Repeated cordocentesis recorded a 30% transplacental crossing of sirolimus. Continuation of sirolimus after birth allowed resection of the residual mass. We have followed the physical and neurological evolution of the child for 6 years since the fetal administration of sirolimus. We conclude that early administration of sirolimus during pregnancy with maternal serum monitoring may be proposed to high-risk fetal LMs in selected cases.