The incidence of clinically detected prostate cancer is increasing with more frequent diagnosis in younger male patients. Whether this represents a genuine increase in incidence or earlier detection is not clear. To understand better the evolution and early changes of prostate cancer we evaluated 152 prostate glands from young male patients 10 to 49 years old. Of the prostates 98 were from African-Americans and 54 were from white patients. Prostatic intraepithelial neoplasia was identified in 0%, 9%, 20 and 44%, and small foci of histological cancer in 0%, 0%, 27% and 34% of the male patients in the second, third, fourth and fifth decades of age, respectively. The majority of the cases of prostatic intraepithelial neoplasia were of low grade. High grade prostatic intraepithelial neoplasia, found in 5 prostates, was first identified in the fifth decade. All 5 cases occurred in prostates containing histological carcinoma. Incidental carcinoma was detected with a similar frequency in white and black patients. The cancerous foci were of similar size with a tendency for cancer in black patients to be multifocal, particularly in those in the fifth decade. We conclude that prostatic intraepithelial neoplasia and histological cancers are surprisingly common in young male patients of both races. The evolution of prostatic intraepithelial neoplasia and focal histological cancers is not clear but it appears to present several decades earlier than clinically detected carcinoma. The natural history of prostate cancer must encompass many more years (decades) than has been previously realized. In addition, the initiating events leading to clinically relevant prostate cancers likely occur at a remarkably young age.