We report a case of hypertrophic olivary degeneration (HOD) detected by MRI, in a 14-year-old girl, 13 months after surgical excision of a brainstem cavernous malformation. As in vivo diagnosis of this condition has only become possible with the advent of MRI, the number of reported cases remains relatively small and they are almost exclusively in adults. Many radiologists and particularly paediatric radiologists, may therefore be unfamiliar with this entity. To our knowledge, this is the first specific report of HOD diagnosed by MRI in a child.