A rare thyroid tumour is described. It started as a papillary cytoadenoma 20 years ago, followed by the appearance of a papillary adenocarcinoma 6 years later. At that time most of the tumour was excised, except for a small portion which had invaded the trachea. Post-operatively 6,000 rads of Co60 was given to the neck; the tumour remained quiescent for 18 years until two years ago, when a recurring fibrosarcoma appeared in her neck. It is suggested that this tumour was a radiation-induced sarcoma.