It is well established that adjuvant treatment reduces mortality after early breast cancer. However, the optimal timing of adjuvant treatment is not well described. To determine the optimal timing of adjuvant treatment, 402 breast cancer patients who received adjuvant treatment at Ankara Oncology Research and Training Hospital between January 1995 and August 2002 were evaluated retrospectively. Three hundred and fifty-seven (88.8%) patients received adjuvant chemotherapy, 204 (50.7%) of these patients received only adjuvant chemotherapy and 153 (38%) patients received tamoxifen following chemotherapy. Remaining 45 (11.2%) patients received only adjuvant tamoxifen. The median time to start adjuvant treatment after surgery was day 21 (range, days 4 to days 258), and the median follow-up was 50 months (range, 6-105 months). The patients were divided into 5 groups according to starting time of chemotherapy (shorter than 14 days, between days 15-29, between days 30-44, between days 45.-59 and more than 59 days). Overall survival (OS) and disease-free survival (DFS) were not shown significantly different between for 5 groups (P > 0.05). Secondly, patients were divided into two groups as starting adjuvant treatment equal to or shorter than 44 days and longer than 44 days (n = 344, 85.6% and vs. n = 58, 14.4%, respectively). OS was significantly better in patients who started to receive adjuvant treatment within 44 days after surgery compared to patients who received adjuvant treatment after 44 days (92 vs. 83.3%, P = 0.03) for 5 years, but DFS was not significantly different between two groups (83.4 vs. 82.2%, P > 0.05). According to our study, adjuvant treatment of breast cancer should be initiated earlier after surgery.