Background. The role of tissue inhibitor of metalloproteinases-1 (TIMP-1) in estrogen receptor (ER) positive breast cancer remains to be fully elucidated. We evaluated TIMP-1 as a prognostic marker in patients treated with adjuvant tamoxifen and investigated TIMP-1s association with Ki67 and ER/progesterone receptor (PR)/human epidermal growth factor receptor 2 (HER2) profiles. Material and methods. TIMP-1 expression was evaluated by immunohistochemistry (IHC) on formalin fixed paraffin embedded primary tumor tissue in two independent cohorts comprised of 236 and 192 patients, respectively. Results. No differences in disease free survival (HR 0.98; 95% CI 0.63-1.53; p = 0.92) and overall survival (HR 0.94; 95% CI 0.63-1.43; p = 0.79) were observed according to TIMP-1 status. A significant negative association between TIMP-1 and Ki67 was identified (p = 0.015). TIMP-1 expression did not differ significantly according to ER/PR/HER2 profiles. When analyzed as separate variables PR and HER2 status tended to have a positive but non-significant association with TIMP-1 (PR: p = 0.08; OR 2.54; 95% CI 0.91-7.10, HER2: p = 0.08; OR 0.48; 95% CI 0.21-1.08) whereas ER status was not associated with TIMP-1 expression (p = 0.48; OR 0.68; 95% CI 0.23-1.99). Conclusion. TIMP-1 does not appear to be prognostic in breast cancer patients receiving adjuvant tamoxifen. We identified a negative association between TIMP-1 and Ki67. We did not confirm our previous in vitro findings of a negative association between TIMP-1 and PR.