Both the histological grade of the primary tumour and lymph node status have been found to contribute significantly towards the development of a local or regional recurrence after simple mastectomy for operable breast cancer. No other factor, from a series of seven studied, has been found to be of independent significance. A small group of patients with grade III tumours, lymph node positive at mastectomy, has been identified in whom more than 40 per cent of all symptomatic local or regional recurrences occurred. The chance a patient in this group has of developing a local or regional recurrence requiring treatment within 4 years approaches 50 per cent.