Prostatic carcinoma is a common and growing public health problem. Cyclin Dı is a cell regulatory protein, which is believed to play an important role in both tumorgenesis and grading of many cancers. The role of Cyclin D1 as a prognostic factor in cancer prostate is controversial.The present study was done on a total of forty cases of prostatic carcinoma removed by radical prostatectomy. Immunohistochemical expression of Cyclin D1 was evaluated in all cases. Correlation between the intensity of Cyclin D1 expression and patient's age, serum PSA level, PIN, Gleason grades, Gleason scores and stages of prostatic carcinoma was evaluated.All cases (100%) revealed foci (>10 % of cancer cells) with positive nuclear staining for Cyclin D1 with different grades of intensity ranging from moderate to strong, while positive Cyclin D1 expression was observed in the nuclei of PIN of 30 cases with grades of intensity ranging from weak to strong. No significant correlation was found between the intensity of Cyclin D1 expression and patient's age, PIN, Gleason grades, Gleason scores or stages of prostatic carcinoma, while a significant correlation between intensity of expression of Cyclin D1 and preoperative serum PSA level was observedCyclin D1 expression might affect PSA expression, which is considered an important tumor marker. Cyclin D1 plays an important role in the pathogenesis and evolution of prostate cancer rather than the prognosis, thus Cyclin D 1 is not a reliable prognostic factor in cancer prostate.