A 6-year-old girl presented with a grossly expansive lesion of the left lower jaw. Radiological investigations revealed a large mixed radiolucent/radio-opaque lesion of the left mandible extending into the ramus. Correlation of biopsy and imaging results lead to the diagnosis of an expansile form of focal cemento-osseous dysplasia. Surgical enucleation was performed, and the patient remained free of recurrence after 6 months of follow-up. When dealing with fibro-osseous lesions of the jaw, correlation of radiological and pathological results is mandatory to make a correct diagnosis and avoid unnecessarily extensive surgery.