To assess the practical prognostic value of pS2, we evaluated its expression by immunohistochemistry in paraffin-embedded tissue from 942 previously untreated invasive ductal carcinomas (IDC) resected in our center between 1980 and 1986. Positive staining of tumor cells was found in 684 cases (73%), but most of the tumors contained only a small amount of positive cells. There was a negative correlation between pS2 and tumor size (p = 0.01) and histological grade (p < 0.0001), and a positive correlation between pS2 and hormonal receptor status (p < 0.001). With respect to overall survival, pS2 positivity was associated with a better prognosis for the whole group and the node-positive sub-group. However, in terms of relapse and metastasis, pS2 was not significant. Furthermore, in multivariate analysis including tumor size, nodal status, histological grade, ER status, PR status, chemotherapy, hormonal treatment, and pS2, the latter appears to be of no prognostic value.