p63 expression was evaluated in a tissue microarray of prostate tissues including benign glands, prostatic intraepithelial neoplasia and prostatic carcinoma. Immunostaining with anti-p63 antibody was restricted to basal cell nuclei. Detectable p63 was found in immortalized and early passage cell cultures, but not in senescent cultures or metastatic tumor-derived cell lines. The selective presence of p63 in basal cells of the prostate suggests that p63 can be used as a marker of basal cells and in vitro typing cell cultures of prostate cancer (CaP). The basal cell association underscores its critical functions in the biology of basal cells.