The relationship of prostatic intraepithelial neoplasia (PIN) and invasive carcinoma of the prostate is not fully understood. It is generally accepted that HGPIN is a probable preinvasive malignant change or at least a marker lesion for carcinoma. The prevalence of HGPIN in younger men is not known. Two hundred and forty nine entirely processed prostates from men aged 20-69 were thoroughly evaluated for the presence of PIN and carcinoma. The histologic diagnosis of all positive cases was confirmed by two pathologists. Our results are summarized as follows: Seventy seven percent of the prostates with HGPIN harbored adenocarcinoma, whereas the frequency of cancer in prostates without HGPIN was 24%. HGPIN was encountered in 0, 5, 10, 41 and 63% of men in the 3rd, 4th, 5th and 7th decades, respectively. The corresponding figures for invasive carcinoma were 2, 29, 32, 55, and 64% respectively.