Background: Monteggia fractures are uncommon injuries in paediatric age. Treatment algorithms assert that length-unstable fractures are treated with plate fixation. In this case report, intramedullary fixation of an acute length-unstable Monteggia fracture allowed a stable reduction to be achieved, along with an appropriate ulnar length and alignment as well as radio capitellar reduction despite the fact that the orthopaedic surgeon did not use a plate for the ulnar fracture.