In this study we investigated the role of the polymorphic types of CYP2D6 in the Turkish population for therapeutic efficacy among patients with early stage breast cancer who treated with tamoxifen. CYP2D6 plays an important role in tamoxifen metabolism. CYP2D6 genotypes were determined of 115 patients treated with adjuvant tamoxifen using the AmpliChip CYP450 test. Genotypes were classified by metabolizer groups and evaluated by the diagnostic and clinical characteristics of the patients and the recurrences of the disease. To create an intergroup comparison of the categorical measurements, the Chi-Square test was used. The most common CYP2D6 gene polymorphism was *1/*2 with a percentage of 19.9% (n= 19). In the Turkish population, among patients with early stage breast cancer, the normal metabolizer group was the largest with a percentage of 77.1% (n= 74). The percentage rates were determined to be 11.5% (n= 11) for intermediate metabolizers, 5.2% (n= 5) for ultrarapid metabolizers and 2.1% (n= 2) for poor metabolizers. In patients with early stage breast cancer treated with adjuvant tamoxifen. no significant correlation was detected between CYP2D6 types and recurrence and metastasis rates. This study was the first study to determine CYP2D6 genotypes and characteristics of Turkish patients with early stage breast cancer. Although no correlation was demonstrated between CYP2D6 genotype polymorphism and disease recurrence in the earlier period, long-term follow-ups seem to be warranted.