P53 immunohistochemical detection using DO7 antibody on 942 cases of previously untreated breast invasive ductal carcinoma (IDC) with a median follow up of 117.9 months (89 to 160) was performed. Three hundred and three (32%) tumors were positive. All positive tumors were taken into account, positivity ranging from 1 to 100% of tumoral cells. The Chi square test showed significant negative correlation between p53 positivity and age (p = 0.01), estrogen receptor status (p < 0.0001), and progesterone receptor status (p = 0.0005), and significant positive correlation with tumor grade according to the Scarff, Bloom and Richardson system (SBR Grade) (p < 0.0001). There was no significant association with tumor size or nodal status. Concerning the univariate analysis, in the whole group and node-positive group (n = 544) p53 positivity was highly significant for overall survival (OS) (p < 0.0001 and p = 0.0003), disease-free interval (DFI) (p = 0.0001 and p = 0.0005), and metastasis-free interval (MFI) (p < 0.0001 and p = 0.0003). In the node-negative group (n = 398), p53 was significant with respect to OS (p = 0.01) and DFI (p = 0.04). P53 positivity came out as an independent prognostic parameter in the multivariate analysis in the whole group and the node-positive group, though of minor significance compared to axillary lymph node status, SBR grade, progesterone receptor status and tumor size.