Prostate specific antigen is a 33 kiloDalton gylcoprotein which was originally believed to be a tissue specific protein produced! by epithelial cells of the prostatic gland. Its functions as a serine protease and is utilized as a tumor marker and screening tool for prostatic carcinoma. Recently the presence of immunoreactive prostate-spedfic-antigen (IR-PSA) has been reported in extraprostatic tissues including breast , liver , ovary , adrenal and parotid glands . The reason for extra-prostatic expression of PSA in breast tissue is not known . It has been suggested that PSA may act as a growth factor or a regulator of growth factors. In seminal plasma , PSA has been shown to proteolyze insulin-like growth factor binding protein 3 (IGF.BP-3) and to prevent the binding of insulin-like growth factor (IGF) binding. However , no association between PSA and IGFs or IGIBPs have been found in breast tissue studies. Patients and methods: A 40 cases of breast lesions were collected and these cases involved 30 cases collected retrospectively from the Department of Pathology of Al-Kadhemyia Teaching Hospital for the period between April 2004-2005 and 10 cases collected prospectively from private labs. Formalin fixed paraffin embedded materials were retrieved. In each case one representative section was stained withH and E and two other slides were stained immunohistochemically for PSA. Immunohistochemical staining was done by using PSA monoclonal antibody. For the evaluation of the PSA expression a senaquantitativc evaluation system was used to register the staining intensity and the numbers of positive cells. Results The mean age of the patients was (43.38) years , with a range of (28-66 years). Most of cases (52.5%) had tumor size more than 5 cm. In this study PSA immunoreactivity of tissues from 40 women with breast tumors was 40% . The expression of PSA was found to be 50% in benign cases while in malignant cases it was only 36.6% . For the ductal carcinoma (8) cases (34.78%) out of 23 were PSA positive and (15) cases were negative while for lebular carcinoma (3) cases (42.85%) out of 7 cases were positive for PSA . PSA expression was higher in moderate then well differentiated in both ductal and lobular carcinoma. PSA expression was higher in negative lymph node involvement (46.1%) than positive lymphatic involvement (29.5%). Conclusions 1- PSA expression was higher in benign tumors than malignant breast tumors. 2- There was no significant correlation between PSA and different prognostic factors including : Age , menopausal status,tumor size, hitological grading ,lymphatic involvement, vascular infilteration, lymphocytic infilteration.