Pancreatic duodenal homeobox 1 (PDX-1), a Hox type transcription factor, is necessary for differentiation of exocrine and endocrine pancreas, and regulates insulin gene transcription. PDX-1 expression was studied by immunohistochemistry on a tissue microarray (TMA) of 289 primary prostate cancers (PCa) from radical prostatectomy (RP) specimens with median follow-up of 48.9 months. We separately arrayed benign prostatic tissue, atrophy, high-grade prostatic intraepithelial neoplasia (HGPIN) and PCa from 40 men and also 17 lymph node metastases. Intensity and extent of immunoreactivity and their product (IRp) were evaluated by two independent observers. PDX-1 was overexpressed in cancer vs benign tissue (p<0.001), but also in atrophy and HGPIN vs cancer (p<0.001 and p=0.022, respectively). PDX-1 expression did not correlate with biochemical recurrence, but decreased with higher Gleason pattern (p<0.001) and in metastases vs primary PCa (p<0.001). Weighted kappa for interobserver agreement of intensity, extent and IRp was 0.65, 0.13 and 0.54, respectively. Presence of PDX-1 protein in benign and malignant prostatic tissue was confirmed by Western blot. In view of recent attention to the role of insulin systems in men with PCa, this protein is of interest in the pathogenesis of PCa.