Repeat lengths of the CAG and GGN microsatellites in exon 1 of the androgen receptor (AR) gene have been hypothesized to be associated with prostate cancer risk. In vitro studies have showed an inverse association between AR CAG and GGN repeat length and activity levels of the AR product. It is known that men of African descent have a higher incidence of and greater mortality from prostate cancer than men of Caucasian or Asian descent and, on average, a smaller number of repeats at AR CAG and GGN. Consistent with these findings, studies have also found increased AR protein expression levels in benign prostatic hyperplasia and prostatic diseased tissues from men of African descent. Despite these findings, limited studies have been conducted to evaluate the association between repeat lengths at AR CAG and prostate cancer risk in African Americans. Our study is the first such study to examine whether repeat length of the AR GGN repeat is associated with prostate cancer risk in African Americans. We found no evidence for an association between AR CAG or GGN repeat lengths and prostate cancer risk in a population-based sample of African Americans.