Triple-negative breast cancer (TNBC) accounts for 15-20% of all breast carcinomas and represents an aggressive variant with a high mortality rate. PD-L1 is a protein that plays a pivotal role in suppressing the adaptive immune system. It has become a central target of the immunotherapy approach. Determining the PD-L1 status can identify TNBC patients who may benefit from targeted therapy. This study was performed to estimate the prevalence of PD-L1 expression among Polish TNBC patients. A total of 123 patients with TNBC were tested for PD-L1 expression using immunohistochemical studies. The PD-L1-positive tumors were found in 55 patients (45%), while PD-L1-negative tumors were found in 68 patients (55%). The PD-L1 positive tumors included 17 patients (31%) with the expression covering up to 1% of tumor area, 23 patients (42%) covering 2-5%, 8 patients (14%) covering 6-10% and 7 patients (13%) covering more than 10% of tumor area. The PD-L1 negative tumors included 17 patients (25%) with the expression covering less than 1% of tumor area and 51 patients (75%) with a complete lack of expression. There were no significant differences between the groups with different status of PD-L1 and the clinical tumor and lymph node stages as well as the patients’ age.