The results after 6 years of a prospective clinical trial of adjuvant chemotherapy with a regimen of two drugs—cyclophosphamide and 5‐fluorouracil (CF)— for 2 years in 97 women with stage II or III breast cancer are reported. Eligible patients were free from distant metastases. All patients began adjuvant therapy within 4 weeks of surgery; therapy consisted of radical, modified, or extended radical mastectomy. No postoperative radiotherapy was given. The results are compared with a historical control group from previous consecutive patients treated by surgery alone. Patients were stratified by age (younger than 50 or older than or equal to 50) and nodal status (one to three positive axillary nodes vs. four or more positive nodes). The estimated 6‐year survival was 60% for CF patients vs. 31% for control patients (P = 0.001). The estimated 6‐year disease‐free survival was 53.6 and 30.3% for CF and control, respectively (P = 0.007). There was a trend toward longer disease‐free survival (DFS) and survival (S) in patients treated with CF, but this was not significant in all the subgroups. Disease‐free survival was statistically significant in the subgroup of women ≥ 50 years old with one to three positive nodes (P = 0.038); survival in the patients ≤ 49 years old with four or more positive nodes (P = 0.0036); and in patients ≥ 50 years old with one to three lymph nodes involvement (P = 0.038). Copyright © 1988 Wiley‐Liss, Inc., A Wiley Company