Massive acute thymic haemorrhage in the neonate occurs extremely rarely and is associated with haemorrhagic disease of the newborn. A 30 year old woman with an unremarkable previous obstetric history presenting at 37 weeks and 4 days gestation with the complaint of loss of fetal movement was found to have a male fetus with findings at necropsy of massive acute thymic haemorrhage, acute intracranial haemorrhage, and hydrops fetalis. This is the first report of massive acute thymic haemorrhage in utero. Massive thymic haemorrhage should be added to the reported causes of lethal non-immunological hydrops.