We report a case of a 29-year-old female patient who suffered from visual disturbance, resulting from a lesion in the sphenoid bone which, histologically, proved to be a giant cell tumour. Reviewing our laboratory practice over a 50 year period, only 7 cases of true giant cell tumour were found and they were in two major locations, i.e. the skull and vertebrae. These few cases led us to focus on the problem raised by the lack of histological patterns of malignancy. In agreement with Mazabraud's theory, it seems that a vertebral location is associated with a good prognosis and that gene mapping of chromosome 17 in relation to p53 mutations could be a valuable tool in the diagnosis of potential malignant behaviour.