Purpose: The purpose of this study was to retrospectively evaluate the expression of BAG-1 in invasive breast carcinomas. The intensity and subcellular distribution of BAG-1 expression was correlated with conventional prognostic factors and with disease-free and overall survival. Patients and Methods: One hundred forty patients diagnosed with invasive breast cancer in St. John's, Newfoundland, between 1986 and 1996 were included in the study. The median follow-up of the study was 8 years. Expression of BAG-1 was determined by immunohistochemical staining of paraffin-embedded breast tumor tissues. Results: Of the 140 breast carcinomas examined, 77.1% were positive for BAG-1 expression. Except for differentiation, no correlation was observed between BAG-1 expression and conventional prognostic factors such as age, histology, stage, and estrogen and progesterone receptor status. In multivariate analysis, BAG-1 expression was significantly associated with shorter disease-free (P = .0052) and overall survival (P = .0033). Patients whose tumors expressed nuclear BAG-1 tended to have a shorter disease-free (63 v 84 months; P = 0.4493) and overall (69 v 99 months, P = .1009) survival. Conclusion: BAG-1 is overexpressed in the majority of invasive breast carcinomas. Although BAG-1 did not correlate with conventional prognostic factors, its overexpression, especially the nuclear expression, may be associated with a shorter disease-free and overall survival. Our preliminary data strongly indicate that further investigation is warranted to define the role of BAG-1 as an independent prognostic factor in patients with newly diagnosed breast cancer.