BACKGROUND Breast tumours are classified as benign, proliferative and invasive tumours. Estrogen hormone influences the proliferative activity and progression of the tumour. Estrogen Receptor (ER) status and proliferative index (Ki 67) are important histopathological factors in the development and prognosis of these tumours. OBJECTIVE The present study was aimed to evaluate the variations in ER and Ki-67 expression in three broad categories of breast lesions namely benign breast disease, proliferative breast disease and malignant breast disease. METHODS ER% and Ki-67% was evaluated on the histopathological tissues of 15 patients each of benign, proliferative and invasive breast tumours. The ER+/ Ki-67± ratio was calculated and the variation of expression between the three categories was analyzed using student's t-test. Pearson's coefficient of correlation was used to correlate ER and Ki-67 positivity within each category. RESULTS The mean ER+/Ki-67+ in benign, proliferative and invasive tumours was 0.81, 0.87 and 1.42 respectively. A statistically significant difference in ER+/Ki-67+ proportions was observed between proliferative breast disease category and malignant breast disease category and also between benign breast disease category and malignant breast disease category (p<0.05). However, no significant difference was observed in benign breast disease category and proliferative breast disease category (p>0.05). A significant correlation was observed in proliferative breast disease and malignant breast disease categories. However, no significant correlation was observed in benign breast disease category. CONCLUSIONS ER+/Ki-67+ ratio is an important determinant of the invasive breast cancer and can be used to differentiate invasive cancers from benign and proliferative breast tumours.