From 1977 to 1982 a total of 2,935 women with breast cancer fulfilled the criteria for inclusion in the low-risk protocol of the Danish Breast Cancer Cooperative Group, DBCG 77-A. The operation performed was a total mastectomy with axillary dissection slightly modified according to Cady. Postoperatively the patients were examined clinically and by chest radiography with intervals for ten years or until recurrence. With a median observation time of seven years loco-regional recurrence appeared in 409 patients (13.9%): chest wall 9.3%, axilla 3.7%. Half of the recurrences were diagnosed within two years postoperatively. Metastases appeared in 396 patients (13.5%), mainly in bones and lungs; 96 patients (23.5%) with loco-regional recurrence and 174 (43.9%) with distant metastases died from breast cancer during the observation time. Life-table analyses of recurrence-free survival (61.7%) and survival (75.4%) are presented. The results of the treatment are in accordance with reports in the literature, but a straightforward comparison is impossible on account of a huge variation in surgical and postsurgical treatment. Finally, the surgical technique in the participating departments in this nation-wide study was evaluated. A high grade of uniformity with respect to loco-regional recurrences was found.