PURPOSE To determine whether the Recurrence Score (RS) provided independent information on risk of distant recurrence (DR) in the tamoxifen and anastrozole arms of the Arimidex, Tamoxifen, Alone or in Combination (ATAC) Trial. PATIENTS AND METHODS RNA was extracted from 1,372 tumor blocks from postmenopausal patients with hormone receptor-positive primary breast cancer in the monotherapy arms of ATAC. Twenty-one genes were assessed by quantitative reverse transcriptase polymerase chain reaction, and the RS was calculated. Cox proportional hazards models assessed the value of adding RS to a model with clinical variables (age, tumor size, grade, and treatment) in node-negative (N0) and node-positive (N+) women. RESULTS Reportable scores were available from 1,231 evaluable patients (N0, n = 872; N+, n = 306; and node status unknown, n = 53); 72, 74, and six DRs occurred in N0, N+, and node status unknown patients, respectively. For both N0 and N+ patients, RS was significantly associated with time to DR in multivariate analyses (P < .001 for N0 and P = .002 for N+). RS also showed significant prognostic value beyond that provided by Adjuvant! Online (P < .001). Nine-year DR rates in low (RS < 18), intermediate (RS = 18 to 30), and high RS (RS > or = 31) groups were 4%, 12%, and 25%, respectively, in N0 patients and 17%, 28%, and 49%, respectively, in N+ patients. The prognostic value of RS was similar in anastrozole- and tamoxifen-treated patients. CONCLUSION This study confirmed the performance of RS in postmenopausal HR+ patients treated with tamoxifen in a large contemporary population and demonstrated that RS is an independent predictor of DR in N0 and N+ hormone receptor-positive patients treated with anastrozole, adding value to estimates with standard clinicopathologic features.