Haemorrhagic-aneurismal bone cysts (HABCs) are quite rare, benign, non-neoplastic, expansive, and vascular locally destructive lesions. They are generally considered sequelae of an earlier trauma causing an overflow of blood into the bone. HABCs are classified as pseudocysts and they should be differentiated from true cysts because their treatment is different. Since few of these cysts involve subjective symptoms, most are discovered accidentally during radiography, while a sure diagnosis is likely to be obtained only during surgery, on discovery of a non-epithelialised cavity. Here, we report a typical case of a haemorrhagic-mandibular cyst in a 13-year-old girl, which was treated by opening the cavity and scraping its walls following diagnostic arteriography and post-operative transcutaneous intralesional embolization. No further complications were recorded in the post-operative period, although the convalescence lasted for a time longer than expected, because of anemia. No further surgery was performed. She has been disease-free for two years. Evaluation of intralesional blood flow is important for HABCs because of the hemorrhagic risk in surgery. Embolization seems to be a useful procedure in the treatment of HABCs and could be tried as the treatment modality in the standard protocol for the treatment of HABCs.