Variations in transcriptional activity of the androgen receptor (AR) are related to polymorphic CAG and GGC repeats in exon 1 of the AR gene. We investigated the association between CAG and GGC repeat length and the risk of prostate cancer in a case-control study from a Brazilian population. We evaluated 49 patients and 51 healthy controls. DNA was extracted from peripheral leukocytes and the AR gene was analyzed by fragment analysis (GeneMapper software, Applied Biosystems, Foster City, California, USA). CAG and GGC mean lengths were not different between cases and controls. The risk for prostate cancer was higher for CAG repeats < or = 21 (OR = 2.44 [95% CI 1.03-5.81]) as well as for total repeat lengths (CAG + GGC) < or = 37 (OR = 2.46 [95% CI 0.98-6.18]). GGC repeats (< or = 17 and > 17) were not associated with risk for prostate cancer (OR = 1.13 [95% CI 0.47-2.75]). In conclusion, fewer number of CAG repeats and total repeats (CAG + GGC) in the AR gene may be associated with increased risk for prostate cancer.