Chemotherapy regimens that combine anthracyclines and taxanes result in improved disease-free and overall survival among women with operable lymph-node-positive breast cancer. The effectiveness of concurrent versus sequential regimens is not known. We randomly assigned 5351 patients with operable, node-positive, early-stage breast cancer to receive four cycles of doxorubicin and cyclophosphamide followed by four cycles of docetaxel (sequential ACT); four cycles of doxorubicin and docetaxel (doxorubicin-docetaxel); or four cycles of doxorubicin, cyclophosphamide, and docetaxel (concurrent ACT). The primary aims were to examine whether concurrent ACT was more effective than sequential ACT and whether the doxorubicin-docetaxel regimen would be as effective as the concurrent-ACT regimen. The secondary aims were to assess toxic effects and to correlate amenorrhea with outcomes in premenopausal women. At a median follow-up of 73 months, overall survival was improved in the sequential-ACT group (8-year overall survival, 83%) as compared with the doxorubicin-docetaxel group (overall survival, 79%; hazard ratio for death, 0.83; P=0.03) and the concurrent-ACT group (overall survival, 79%; hazard ratio, 0.86; P=0.09). Disease-free survival was improved in the sequential-ACT group (8-year disease-free survival, 74%) as compared with the doxorubicin-docetaxel group (disease-free survival, 69%; hazard ratio for recurrence, a second malignant condition, or death, 0.80; P=0.001) and the concurrent-ACT group (disease-free survival, 69%; hazard ratio, 0.83; P=0.01). The doxorubicin-docetaxel regimen showed noninferiority to the concurrent-ACT regimen for overall survival (hazard ratio, 0.96; 95% confidence interval, 0.82 to 1.14). Overall survival was improved in patients with amenorrhea for 6 months or more across all treatment groups, independently of estrogen-receptor status. Sequential ACT improved disease-free survival as compared with doxorubicin-docetaxel or concurrent ACT, and it improved overall survival as compared with doxorubicin-docetaxel. Amenorrhea was associated with improved survival regardless of the treatment and estrogen-receptor status. (ClinicalTrials.gov number, NCT00003782.)