The association between androgen receptor gene polymorphisms and benign prostatic hyperplasia was investigated among 510 men randomly selected from Olmsted County, Minnesota. From 1990 through 2000, lower urinary tract symptom severity was assessed by the American Urological Association Symptom Index (AUASI), and peak urinary flow rate, prostate volume, and serum prostate-specific antigen level were measured. Androgen receptor CAG and GGN genotyping was performed. A CAG repeat length of <21 was associated with an enlarged prostate (hazard ratio (HR) = 1.4, 95% confidence interval (CI): 1.0, 1.9) and a serum prostate-specific antigen level >1.4 ng/ml (HR = 1.5, 95% CI: 1.1, 2.0). A GGN repeat length of <16 was associated with an AUASI >7 (HR = 1.6, 95% CI: 1.1, 2.3) and a serum prostate-specific antigen level >1.4 ng/ml (HR = 1.5, 95% CI: 1.0, 2.3). Having <21 CAG repeats and <16 GGN repeats compared with having neither was associated with an enlarged prostate (HR = 2.5, 95% CI: 1.5, 4.2), a serum prostate-specific antigen level >1.4 ng/ml (HR = 2.8, 95% CI: 1.6, 4.7), a peak flow rate <12 ml/second (HR = 1.9, 95% CI: 1.1, 3.4), and an AUASI >7 (HR = 1.6, 95% CI: 1.0, 2.7). Androgen receptor gene polymorphisms may have a potential role in the pathogenesis of benign prostatic hyperplasia.