The results of a prospective study over 20 years of 193 patients with breast carcinoma treated by Patey mastectomy are presented together with details of the operative technique employed. One hundred and twenty-eight cases (66%) were stage 1 (T1/T2 N0), 46 (24%) were stage 2 (T1/T2 N1), 18 (9%) were stage 3 (T3 N0/N1), and one was stage 4 (M1). The probability of survival together with 95% confidence intervals for stage 1 (T1/T2 N0) at 10 years was 79% (71-88); and at 15 years 74% (61-87). For stage 2 (T1/T2 N1), the probability of survival at 10 years was 64% (48-79), and at 15 years 60% (44-76). For stage 3 (T3 N0/N1), the probability of survival at 10 years was 70% (45-95) and nobody survived at 15 years. These differences between the clinical stages lacked significance [Log-rank test: chi 2 = 3.44 df = 2 P = 0.18]. There were nine patients (5%) who developed local recurrence without systemic metastases. There was no postoperative mortality, and morbidity was low. Axillary node metastases depressed survival with probability of survival at 10 years 43% (29-57) in contrast to those without it 90% (84-96) [log-rank test: chi 2 = 39.42 df = 1 P < 0.0001]. Patey mastectomy should be considered for patients with T1 or T2 tumours who choose mastectomy rather than breast conservation. It is an effective local treatment which is of particular relevance in countries where radiotherapy is not available.