The aim of the study was to evaluate the number of circulating endothelial progenitor cells (circulating EPCs) in the blood of patients diagnosed with breast cancer and to make an attempt at finding associations with the number of circulating EPCs and selected clinic-pathological factors; TNM and histological grading, molecular subtype of breast cancer, hormonal status, the expression of Ki-67 and the size of tumour. The study involved 96 Caucasian ethnicity post-menopausal women. Sixty-six women aged 48 - 63 (mean age 55) with breast cancer diagnosis without distant metastases (M0). The median value of the tumour diameter was 1.51 cm. The control group consisted of 30 healthy, non-smoking, post-menopausal women, mean age 49, range 44 - 54 years of age. The exclusion criteria for all the participants were hypertension, hyperlipidaemia, and hyperglycaemia, acute and chronic infection. With regard to the fresh blood samples the number of circulating endothelial progenitors was determined using flow cytometry. The fluorescence of 100,000 cells was measured during the analysis. Circulating EPCs were identified with the immune-phenotype CD45-, CD34+, CD133+, CD31+. A significantly higher number of circulating EPCs in the study group, as compared to the controls (P = 0.0001) and a significantly higher number of circulating EPCs in women over 60 with breast cancer than in the younger women (P = 0.0029) were reported. A positive correlation was noted between circulating EPCs and age as well as between circulating EPCs and HER-2 (P = 0.0231, P = 0.0414, respectively), and a negative correlation between circulating EPCs and histological grading of breast cancer (P = 0.0272). The study has shown a higher number of circulating EPCs in breast cancer patients, which indicates stimulation of neovascularization. Additionally, since bone morrow-derived circulating EPCs are more intensively mobilised in older and overweight breast cancer patients, we can speculate that more aggressive neo-angiogenesis can occur in those patients.