Identification of prostate cancers at high risk of progression is difficult and a better understanding of how peptide growth factors influence cellular function might be useful. Fibroblast growth factors (FGFs) have been implicated in prostate cancer development. FGF8 was identified in the Shionogi mouse mammary carcinoma SC-3 cell line as an androgen-induced mitogen. We tested if FGF8 was over-expressed in human prostate cancer and if its expression correlated with clinical data and outcome. One hundred and six cases of prostate cancer and ten cases of BPH were examined. In situ hybridization was employed to detect FGF8 mRNA expression, which was identified within the malignant prostatic epithelium in 85/106 (80.2%) cases. Increased expression of FGF8 correlated significantly with higher Gleason scores (P=0.0004) and advanced tumour stage (P=0.0016). Using immunohistochemistry, we confirmed over-expression of the FGF8b isoform. Men with tumours which expressed high levels of FGF8 had worse survival (P=0.034), although FGF8 mRNA was not able to provide additional prognostic information in a multivariate analysis. Additionally, FGF8 expression was shown to persist in androgen independent prostate cancer. Using a range of normal adult tissues, FGF8 expression was restricted to neurones and the germinal epithelium in addition to the prostate. In vitro studies demonstrated that in the presence of neutralizing antibody to FGF8b there was significant inhibition of prostate cancer cell growth, confirming the biological significance of FGF8 in prostate carcinogenesis.