The prevalence of high grade prostatic intraepithelial neoplasia (HGPIN), the age at which this lesion starts and the potential racial or ethnic differences in its distribution are poorly documented. HGPIN is becoming increasingly implicated as a premalignant lesion for clinically significant prostatic carcinoma (PCa) with mounting evidence linking it to carcinoma according to morphologic immunohistochemical and recent genomic studies. We describe our experience with the age and race distribution of HGPIN resulting from two study populations of African-American (AA) and Caucasian (C) males. The first component of this report describes an autopsy study aimed at determining the prevalence of latent PCa and HGPIN in AA and C men 20 years of age or older; 370 (218 AA and 152 C) consecutive step-sectioned, totally embedded prostate glands were microscopically evaluated and mapped for HGPIN and PCa. HGPIN was first identified in the third decade and increased steadily with age. Latent PCa increased steadily with age with no significant difference in the prevalence between AA and C males in any age group (3rd to 8th decades). HGPIN, on the other hand, was more prevalent in AA men with 18, 31, 69, 78 and 86% in their 4th, 5th, 6th, 7th and 8th decades harboring the lesion. The corresponding figures for C men were 14, 21, 38, 50 and 63% respectively. When HGPIN was quantitated as focal and extensive according to the degree of glandular involvement, extensive HGPIN appeared earlier in AA males under 60 years of age compared to C males cohort. The difference in age distribution appeared to follow a chronological pattern, with HGPIN in AA preceding that of C males by approximately a decade. The second component of this report describes a surgical series of 345 consecutive radical prostatectomies from patients (155 AA and 190 C) with clinically localized PCa, which were thoroughly evaluated microscopically by two urologic pathologists. Similar to the findings in the autopsy study, extensive HGPIN was more prevalent in AA men 60 years of age or younger (57% vs. 33%). In both races, the mean percentage of the gland involved by HGPIN decreased with advancing age in contrast to the mean tumor volume that increased with patient age. These findings indicating a different prevalence of HGPIN in the two racial groups may help explain the higher incidence of prostatic cancer in African-Americans.