We retrospectively analyzed the effect of maintenance endocrine therapy (MET) after high-dose chemotherapy with hematopoietic progenitor cell transplant (HDCT) on the progression-free survival (PFS) of patients with hormone-dependent metastatic breast cancer (MBC). One hundred and nine consecutive patients with estrogen receptor (ER) and/or progesterone receptor (PgR)-positive MBC, who were progression free for at least 4 months after HDCT with cyclophosphamide, carmustine and thiotepa (CBT), were analyzed. Of these, 55 were non-randomly submitted to MET. After a median follow-up of 34.4 months (17.1-91.0), univariate analysis showed that MET was significantly associated with improved median PFS (31.1 vs 19.2 months, P = 0.022). Complete response to HDCT, pattern of metastatic spread, extent of the disease, single vs multiple metastatic sites, prior endocrine therapy for metastatic disease and prior exposure to any hormonal therapy (adjuvant and/or for the advanced disease) were also associated with PFS at univariate analysis. A multivariate Cox proportional hazard model was fitted to the data in order to correct the effect of MET for the other significant covariates. After correcting for these covariates, MET was still significant, predicting improved PFS (hazard ratio (HR) 0.580, 95% CI; 0.362-0.931). Administration of MET after optimal cytoreduction might result in increased efficacy of HDCT in hormone-dependent metastatic breast cancer.