SUMMARY We set out in this study to see the pattern of expression of hormones and cell cycle regulatory proteins and to determine the correlation between the expression of various cell cycle proteins and oestrogen/progesterone receptors (ER/PR).One hundred and nineteen (119) selected cases of infiltrating breast cancer between year 2002 and 2005 from the Lagos University Teaching Hospital, Lagos, Nigeria were studied using tissue microarray technique and immunohistochemistry at the Royal Cornwall Hospital, Truro, England. The mean age of presentation of patients with breast cancer was 44.2 years with a preponderance of younger patients who presented with higher grades of breast cancers. In the younger age group (20-39 years), 75.6% presented with ER negative tumours and 88.9% of cases were PR negative. Most low grade tumours were ER/PR positive. Most of our tumours were poorly differentiated and negative for ER/PR expression. There was correlation between the grade of tumours and hormonal status. Furthermore there was a trend that higher grade tumours showed less p53 altered expression. We found that 31.0% of our cases were ER positive and 20.7% were PR positive. The frequencies of positive expression of p16, p21, p27, Cyclin D1 and Cyclin E are 67.8%, 69.5%, 64.0%, 40.9% and 44.0% respectively while 73.5%cases showed altered p53 expression. The study showed that there was a significant association between Cyclin D1 and ER/PR. A significant inverse correlation also existed between Cyclin E and ER but not with PR expression. A significant correlation between ER/PR and p21 and p27. Furthermore, high grade tumours tend to be p16 positive and a significant inverse correlation between p53 and PR status. We suggest the use of Cyclin D1, p16, Cyclin E as indices of prognosis for cases of breast cancer in Nigeria and it is recommended that typing of all our breast cancer cases for ER/PR status is mandatory before hormonal therapy.