Between November 1979 and December 1986, 263 patients were treated for primary breast cancer by local excision and radiotherapy at the City Hospital, Nottingham. Local recurrence within the treated breast occurred in 56 patients (21 per cent), in 18 (6·8 per cent) of whom it was gross and uncontrollable. An analysis of clinicopathological features shows patient age, nodal status, tumour size, presence of definitive vascular invasion, adjacent ductal carcinoma in situ and grade to be predictive of local recurrence. A Cox's multivariate analysis of these factors shows the first four to be independently significant. The factors can be combined as a prognostic index which allows identification of patients at high risk of local recurrence. On the basis of these findings we have altered our selection policy for patients suitable for breast conservation.