The combination of doxorubicin and cyclophosphamide (AC) is a standard adjuvant chemotherapy regimen. Studies of docetaxel and cyclophosphamide (TC) in metastatic breast cancer (MBC) showed promise in MBC. In 1997, we initiated a randomized adjuvant trial of TC compared with standard-dose AC with a primary end point of disease-free survival (DFS). Patients were eligible if they had stage I to III operable invasive breast cancer with complete surgical excision of the primary tumor. Between June 1997 and December 1999, 1,016 patients were randomly assigned to four cycles of either standard-dose AC (60 and 600 mg/m2, respectively; n = 510) or TC (75 and 600 mg/m2, respectively; n = 506), administered intravenously every 3 weeks as adjuvant chemotherapy. Radiation therapy (as indicated) and tamoxifen, for patients with hormone receptor-positive disease, were administered after completion of chemotherapy. Both treatment groups (TC and AC) were well balanced with respect to major prognostic factors. Patients were observed through 2005 for a median of 5.5 years. At 5 years, DFS rate was significantly superior for TC compared with AC (86% v 80%, respectively; hazard ratio HR = 0.67; 95% CI, 0.50 to 0.94; P = .015). Overall survival rates for TC and AC were 90% and 87%, respectively (HR = 0.76; 95% CI, 0.52 to 1.1; P = .13). More myalgia, arthralgia, edema, and febrile neutropenia occurred on the TC arm; more nausea and vomiting occurred on the AC arm as well as one incident of congestive heart failure. At 5 years, TC was associated with a superior DFS and a different toxicity profile compared with AC.