Background: Breast cancer (BC) is regarded as a heterogeneous disease that is classified into various molecular subtypes using gene expression analysis. The aim of this study was to perform a population-based analysis of the prevalence of molecular BC subtypes in Turkish women, and to determine their association with known prognostic and clinicopathological factors. Patients and Methods: A total of 1,025 cases with operable BC, who presented within a 2-year period (2006-2007), were evaluated. Estrogen receptor (ER), Progesterone receptor (PR), and HER2 expression were determined immunohistochemically. Results: 68.3% of patients were ER-positive, and 71.5% were PR-positive. Among the 28.3% of HER2-positive tumors, the majority (19.2%) stained +++. Almost 50% of the tumors were ER+ PR+ HER2-, which makes this the predominant tumor type. For both triple-negative and -positive status, a ratio of approximately 10% was determined. For ER+ PR+ HER2-, tumor histology, tumor stage, and histological grade were found to be correlated. Menopausal status, obesity, tumor histology, histological grade, in-situ component, and lymphovascular invasion were associated with triple-positive tumors. A significant relationship was found between the variables - including histological grade, in-situ component, and involvement of axillary lymph nodes - and triple-negative status. Conclusion: A more thorough understanding of the biological background and underlying mechanisms of BC may allow the development of rational targeted approaches and therapies.