Two cases are presented of malignant tumour of the parotid gland following sialography with Thorotrast, 28 and 45 years previously. Both cases were histologically established as squamous cell carcinoma and the presence of Thorotrast in the tumours was confirmed by autohistoradiography. It is suggested that the tumours may have developed from metaplastic ductal epithelium after many years of exposure to the alpha radiation from Thorotrast deposits in the gland.