The case records of 28 patients with Paget's disease of the nipple treated by radio-therapy alone were reviewed retrospectively. 16 of 19 patients who had no palpable underlying tumour and who were mammographically normal at the time of original treatment remain free of disease with a median follow-up of 5 years 3 months. In this selected group, radical radiotherapy with small fields localised to the involved skin is an effective alternative to mastectomy.