Cyclo-oxygenase-2 (COX-2) is a prostaglandin synthease that catalyses the synthesis of prostaglandin G2 (PGG2) and PGH2 from arachidonic acid. COX-2 plays an important role in tumourigenesis of different carcinoma types and it is thought to take part in breast carcinoma. In this study, the aim was to investigate the relationship of COX-2 with clinical parameters such as menopausal status, tumour size, grade, nodal status, Nottingham prognostic index (NPI), oestrogen receptor(ER), progesterone receptor (PR), human epidermal growth factor receptor type 2 (HER-2/ neu). The patients were divided into two groups, first group (group A) comprised 57 primary breast cancer patients and the second group (group B) comprised control group 27 patients consisting of fibro-adenoma and benign breast disease. In control groups COX-2 (0%) is not over expressed and we observed that high frequency of COX-2 (73.68%) over expressed in breast carcinoma. In high grade, large tumour size and positive lymph node metastasis, COX-2 expression rate was 78.6%, 59.5% and 90.5% respectively. COX-2 expression is directly correlated with ER negative (88.1%, p = 0.001) and also associated with higher NPI value (78.6%, p = 0.006). In invasive ductal carcinoma (IDC) COX-2 over expression had a significant relationship with HER-2/neu over expression (p < 0.001). The results indicated that COX-2 over expression correlates with aggressive phenotypic features, such as high histological grade, large tumour size, higher NPI value, ER negativity and HER-2/neu positivity.