Purpose: The optimal number of axillary nodes to be resected is controversial. This large series investigated the effect of surgery with or without adjuvant radiotherapy among node-negative breast cancer patients in relation to the number of nodes examined. Methods and materials: Node-negative patients from the Saskatchewan registry of 1981-1995 were studied. Because nodal status may be more reliable with more number of nodes examined, we analyzed T1-2 age < 90 patients with < 10 nodes examined treated with surgery alone (Group A_S, n = 509) vs. surgery and adjuvant radiotherapy (Group A_S+R, n = 342); and T1-2 age < 90 patients with > or = 10 nodes examined treated with surgery alone (Group B_S, n = 902) vs. surgery and adjuvant radiotherapy (Group B_S+R, n = 596). Results: For the two radiotherapy groups, patients with < 10 nodes (Group A_S+R) vs. > or = 10 nodes (Group B_S+R), there was no difference in overall survival (p = 0.14). In the two nonradiotherapy groups (A_S and B_S), there is a statistically significant decrease in overall survival for patients with < 10 nodes removed (p < 0.001, log-rank test). The optimal number of axillary nodes examined could be 8 nodes with adjuvant radiotherapy (p = 0.05, logrank test) and 12 nodes without adjuvant radiotherapy (p = 0.02, log-rank test). Conclusions: The poorer prognosis of a lesser number of nodes resected was overcome partly by the use of radiotherapy, raising the possibility of micrometastases in lymph nodes not removed. The optimal number of axillary nodes examined could be 8 nodes with adjuvant radiotherapy and 12 nodes without adjuvant radiotherapy.