A giant paediatric mandibular aneurysmal bone cyst and reconstruction with bilateral iliac bone graft. Aneurysmal bone cyst (ABC) is an unusual, non-neoplastic, expansile lesion of the bone. ABC is not a true cyst and it is characterised by the replacement of bone by fibro-osseous tissue containing blood-filled sinusoidal or cavernous spaces. The expanding mass often disrupts the normal bony architecture, with erosion of the cortex. Surgical treatment consists of complete excision or curettage. In this report, we present a 5-year-old girl with a huge aneurysmal bone cyst in the corpus of the mandible, which was reconstructed with bone graft taken from bilateral anterior iliac crests.