Abstract: Cyclin D1 is involved in regulating the transition of G1 to S-phase in the cell cycle. Amplification and overexpression of the cyclin D1 gene have been reported to be implicated in breast carcinoma and are suggested to play important roles in breast carcinogenesis. In the present study, we tried to evaluate the correlation between cyclin D1 expression and gene amplification and analyze the correlations between cyclin D1overexpression with clinicopathological features in different breast lesions. Cyclin D1 gene amplification and protein overexpression were assessed in 20 cases of ductal hyperplasia without atypia, 20 cases of atypical ductal hyperplasia, 24 cases ductal carcinoma in situ and 114 cases of invasive carcinoma. Cyclin D1 overexpression was found in 0, 30, 58.3 and 63.2%, respectively. While gene amplification was detected in 0, 0, 16.7 and 15.8%, respectively. In ductal carcinoma in situ, no-significant correlations between either cyclin D1 overexpression or amplification and any of clinicpathological features. In cases of invasive carcinoma, cyclin D1 overexpression and amplification showed a strong direct correlation with expression in both hormonal receptors. There was a significant correlation between cyclin D1 expression and good prognostic parameters, including low histological grade (p = 0.04) and small tumor size (p = 0.003). There was a strong correlation between cyclin Dl overexpression and histological tumor type (p = 0.008). In conclusion, amplification and overexpression of cyclin D1 in atypical ductal hyperplasia, ductal carcinoma in situ and invasive carcinoma suggests its role in early and late stages of breast cancer.