p27kip1 is an inhibitor of cyclin dependent kinase involved in cell cycle regulation. The present work aimed at studying the value of p27 expression as a potential prognostic marker in breast duct carcinomas. p27 immunodetection was estimated and correlated with other clinicopathological prognostic factors (tumor size, tumor grade and lymph nodal status) and with other known well established prognostic biological markers (ER, PR and HER2/neu). Our results revealed the significant association of decreased p27 level of expression with a more aggressive tumor phenotype, concluding that p27 could be useful in the assessment of prognosis, especially in those cases in which the commonly used parameters are insufficient, and might ultimately influence the therapy of this disease.