Aneurysmal bone cysts are rare benign lesions of bone tissue, infrequent in craneofacial skeleton with regard to other structures like long bones or the spine. They are composed of sinusoidal and vascular spaces blood-filled and surrounded by fibrous tissue septa. We present a case of a 29-year-old Caucasian male with a big swelling in the left mandible associated to pain and rapid growth. He referred previous extraction of the left inferior third molar. On the X-ray study, an expansive multilocular and high vascularized bony lesion within the mandibular angle was observed. It produced expansion and destruction of lingual and buccal cortex. An incisional biopsy was performed showing a fibrous tissue with blood-filled spaces lesion suggestive of an aneurysmal bone cyst. After selective embolization of the tumour, surgical resection was done with curettage and immediate reconstruction of the defect with an anterior iliac crest graft. Aneurysmal bone cysts are non-neoplastic but locally aggressive tumours with occasional rapid growth that may be differenciated from other multilocular process like ameloblastoma, ossifying fibroma, epithelial cyst, giant cell granuloma and sarcomas. Treatment of choice consists on conservative surgical excision of the mass with curettage or enucleation. When resection creates a big defect, primary surgical reconstruction is recommended.