The purpose of this article is to evaluate the prognostic value of androgen receptor (AR) expression in patients with estrogen receptor (ER)-positive breast cancer, treated with endocrine therapy, with or without the addition of chemotherapy. A consecutive series of 953 patients with ER-positive breast cancer, treated between 1998 and 2003, was selected. Repeated immunohistochemistry confirmed the expression of ER in the tumor of 938 patients. AR expression was measured by immunohistochemistry. The Kaplan-Meier method, logrank test and multivariate Cox models were used to explore the impact of AR expression on time to relapse (TTR) and disease specific survival (DSS) in all patients and in subgroups treated with chemo-endocrine therapy or endocrine therapy alone. AR immunoreactivity was assessable in 859 tumors and positive in 609 (70.9%). AR expression was a significant marker of good prognosis for TTR (P = 0.001) and DSS (P < 0.001). This effect was particularly evident in the group of patients receiving chemo-endocrine therapy (TTR (P = 0.015) and DSS (P < 0.001)). Cox models confirmed AR as an independent variable for both TTR (P = 0.003, HR 0.444, 95%CI 0.258-0.765) and DSS (P < 0.001, HR 0.135, 95%CI 0.054-0.337). Thus, we focused on ER-positive luminal B breast cancer that may be selected for chemotherapy because of their more aggressive immunophenotype. In this subset AR expression identified a group of patients with better prognosis for TTR (P = 0.017, HR 0.521, 95%CI 0.306-0.888) and DSS (P = 0.001, HR 0.276, 95% CI 0.130-0.588). AR expression is an independent prognostic factor of better outcome in patients with ER-positive breast cancers.