Objective: We determined the prognostic factors of patients with triple-negative breast cancer. Material and Method: Two hundred thirteen female patients with triple-negative breast cancer (TNBC) followed in the medical oncology unit of Kartal Doctor Lütfi Kırdar City Hospital between 2005 and 2020 were evaluated retrospectively. Patients’ clinical and demographic features, laboratory findings, and treatments were investigated and their effect on mortality was analyzed. Results: The median age of patients was 52 years. Relapse was observed in 46 (26.6%) patients, 127 patients were followed without progression. During the follow-up period, 57 patients died and 156 patients survived. The median overall survival was 137.2 months in patients with tumor size <2 cm, 109.9 months in patients with ≥2 cm and <5 cm, and 90.5 months in patients with ≥5 cm (p=0.02). Tumor diameter, lymph node positivity, menopausal status, and whether receiving neoadjuvant chemotherapy were determined as factors affecting the overall survival. Conclusion: In accordance with the literature, patients with TNBC showed more aggressive characteristics. Our findings support that TNBC is a heterogeneous disease and highlight the need to define molecular subclasses. We believe that demographic and prognostic data studies with large patient series and determining molecular markers will guide the follow-up and treatment of patients with TNBC.