Multilobular osteochondrosarcoma (MLO) is an uncommon tumour that arises from the flat bones of the skull and, less frequently, from other flat bones. It grows slowly as a hard, lobulated (lumpy) mass that gradually expands, and its name reflects its distinctive microscopic pattern of multiple rounded lobules of bone and cartilage. Despite its often slow clinical progression, MLO has meaningful metastatic potential — approximately half of cases will eventually spread to distant sites, most commonly the lungs. Treatment hinges on surgical removal, and achieving complete excision with clean margins is the single most important prognostic factor. The tumour's skull location can make surgery challenging, and advanced techniques including craniectomy or stereotactic radiation may be needed.