The aim of this study was to compare p53 and p21 mRNA, and proteins levels between fibroadenomas and adjacent normal mammary tissue of women in reproductive age. A transversal study was performed. Fourteen patients who attended the Breast Service of the Hospital de Clínicas de Porto Alegre were assessed and submitted to surgical resection of fibroadenomas. Fragments of the central area of the fibroadenoma and adjacent normal mammary tissue were obtained. mRNA expression for genes p53 and p21 was evaluated by RT-PCR, and protein expression by the western blot. Paired analyses showed higher gene expression of p53 (P = 0.017) and p21 (P = 0.003), and a higher protein expression of p53 (P = 0.001) in fibroadenomas as compared to normal breast tissue. p21 protein expression was not different (P = 0.97) between the fibroadenoma and the adjacent normal mammary tissue samples. These results suggest the participation of p53 in the formation of fibroadenomas. The role of p21 in fibroadenomas remains to be defined.