The present retrospective study aims to determine the clinical value of thymidine labelling index (TLI) together with other established clinical and biological factors in 116 locally advanced breast cancer (LABC) patients treated with anthracycline-based neoadjuvant chemotherapy, surgery, adjuvant chemotherapy and radiotherapy. TLI was determined in 71 LABC patients with a median of 2.62% (0-23.64%) and a mean of 4.71% +/- 5.54. As a result of neoadjuvant chemotherapy, 85 patients (73%) responded to chemotherapy (CT), whereas 31 patients were unresponsive (27%). No relationship has been found between the pretreatment biological variables including TLI, estrogen receptor (ER), progesteron receptor (PgR) status and clinical parameters such as the chemotherapy response rates and axillary lymph node involvement following chemotherapy. Median follow-up was 35 months (18-97 months) and the 3-year overall survival (OS) and disease free survival (DFS) rates were 71.6% and 52.2%, respectively. In univariate analysis, patients with inflammatory breast cancer, high TLI-index (greater than or equal to2.62%), lymph node (LN) positivity or >3 positive lymph nodes following neoadjuvant chemotherapy and without any response to neoadjuvant chemotherapy were found to have worse DFS and OS-rates and high local and systemic recurrence rates. In multivariate analysis, TLI was estimated as the most powerful independent factor affecting the OS in LABC patients among the other established clinical and biological parameters (p = 0.02). These results suggest that TLI is an important independent indicator of clinical outcome in patients with LABC and these patients with high TLI levels require more effective treatment modalities.