Background: The prognostic role of progesterone receptor (PgR) in highly proliferating early breast cancer (BC) is not well established. We retrospectively explored this biomarker in a cohort of patients with highly proliferating tumors enrolled in a phase III trial of adjuvant therapy. Methods: 1066 patients with N- or 1-3 N+ BC were randomized to receive: epirubicin followed by CMF, CMF followed by epirubicin, or CMF alone. Rapidly proliferating tumors were defined by thymidine labeling index (TLI) > 3% or histological grade 3 or S-phase > 10% or Ki67 > 20%. We analyze the subgroup of 466 patients with hormone receptor (HR)-positive tumors treated with sequential epirubicin/CMF regimens followed by tamoxifen and for whom immunohistochemical assessments of estrogen receptor (ER), PgR, HER2 and Ki67 were available. Disease-free (DFS) and overall survival (OS) curves were built with the Kaplan–Meier estimator and compared by logrank test and Cox regression models. Results: PgR expression was significantly associated with ER expression, HER2 status, age and menopausal status, but not with Ki67, tumor size and nodal status. PgR cutoff values of 10% and 20% were chosen based on a Receiver Operating Characteristics analysis and the literature data. DFS and OS figures at 5 and 10 years, as well as the relative hazard ratios, according to the different PgR cutoff values, are reported in the table. Conclusions: Our results confirm the prognostic relevance of PgR expression in a cohort of patients with highly proliferating, HR-positive early BC treated with adjuvant chemotherapy and endocrine therapy.