Poly(adenosine diphosphate [ADP]-ribose) polymerase 1 (PARP1) plays important roles in DNA damage response pathways and is often overexpressed in various human tumors. Currently, the use of PARP inhibitors for breast cancer (BC) therapy is the subject of debate, and there is an urgent need to understand much the expression and prognostic role of the PARP1 protein. The aim was to investigate the clinicopathological and prognostic significance of PARP1 in BC patients. The PARP1 and breast cancer susceptibility gene 1 (BRCA1) protein expressions were evaluated in 114 BCs by immunohistochemistry. Disease-free survival (DFS) and overall survival (OS) were determined based on the Kaplan-Meier method. Our results showed that nuclear PARP1 expression was significantly associated with peritumoral vascular invasion (P = 0.046), chemotherapeutic treatment (P = 0.026), oestrogen receptor (ER; P = 0.013), human epidermal growth factor receptor 2 (HER2; P = 0.003) and BRCA1 (P < 0.001) expression. Survival analyses showed a significant association with clinical outcome in the subgroup of ER-negative patients (P = 0.017 for DFS and P = 0.048 for OS) and in the subgroup of patients treated with chemotherapeutic agents (P = 0.042 for DFS and P = 0.046 for OS). A significant correlation was also found for DFS in patients characterized by tumors without peritumoral vascular invasion (P = 0.022). More importantly, multivariate analyses revealed that high nuclear PARP1 expression was associated with decreased DFS (P = 0.012) and OS (P = 0.026). In conclusion, PARP1 expression may be used as an independent prognostic factor in BC patients. In addition, this study demonstrated that high PARP1 expression may represent a marker of poorer prognosis both for patients with worse clinical outcome and in less aggressive clinical conditions.