Breast cancer is one of the most common cancers and is the leading cause of cancer deaths in women worldwide and in Croatia. There are very large differences in patient survival, which is why there is a need to detect sensitive diagnostic and prognostic markers. Survivin, encoded by the BIRC5 gene, is one of the proteins of cell death inhibitors (apoptosis) and its level is significantly increased in almost all tumors, whereas it is not expressed in normal differentiated tissues of adult organisms. In breast cancer, its expression is associated with increased resistance to chemo- and radiotherapy, higher histologic grade, younger age, tumor size and negative estrogen receptor status. I studied BIRC5 gene polymorphisms and expression of various survivin isoforms in breast cancer by heteroduplex analysis, DNA sequencing, and qRT-PCR. I found eleven BIRC5 gene polymorphisms and their frequencies in patients with breast cancer did not differ significantly from the frequencies in healthy controls. BIRC5 gene polymorphisms do not appear to play a significant role in the development of breast cancer, but it is possible that a larger sample size would show different results. The assumption that by determining the expression level of some isoforms of the BIRC5 gene can be differentiated tumor-free from healthy tissue was confirmed for five of the eight isoforms.