Shorter CAG repeats in the androgen receptor (AR) gene have been associated with increased prostate cancer risk. Aiming to investigate whether the AR CAG polymorphism is associated with an increased relative risk for prostate cancer in our population, genomic DNA from 133 prostate cancer patients and 279 healthy men controls were examined. We found no association between the AR CAG polymorphism and the relative risk of prostate cancer in white Brazilian individuals with a CAG repeat length </=21. Our results show that in the studied population the Asian-descendants have the highest, the white an intermediate and the black a tendency to the lowest CAG repeats rates. We observed a significant correlation between a lower number of CAG repeats and young age at diagnosis (P=0.034). This study is the first to investigate the association between the AR CAG repeat polymorphism and the relative risk of prostate cancer in the Brazilian population.