High-grade prostatic intraepithelial neoplasia (PIN) is the most likely precursor of prostatic carcinoma. PIN has a high predictive value as a marker for carcinoma, and its identification in biopsy specimens warrants repeat biopsy for concurrent or subsequent carcinoma. The only methods of detection are biopsy and transurethral resection; PIN does not significantly elevate serum PSA concentration or its derivatives, nor does it induce a palpable mass, and cannot be detected by ultrasound. Androgen deprivation therapy decreases the prevalence and extent of PIN, suggesting that this form of treatment may play a role in chemoprevention. Radiation therapy is also associated with a decreased incidence of PIN.