['Studies suggest obesity is associated with decreased prostate cancer risk. We hypothesized obesity is biologically associated with increased risk, although this is obscured owing to hemodilution of prostate-specific antigen (PSA) and larger prostate size.', 'We retrospectively studied 441 consecutive men undergoing prostate biopsy between 1999 and 2003 at two equal access centers within the Veterans Affairs Greater Los Angeles Healthcare System. We estimated the association between obesity (body mass index >or= 30 kg/m(2)) and positive biopsy and Gleason >or=4+3 using logistic regression analysis adjusting for multiple clinical characteristics.', 'A total of 123 men (28%) were obese and 149 men (34%) had cancer. Median PSA and age were 5.7 ng/mL and 63.9 years, respectively. Obese men had significantly lower PSA concentrations (P = .02) and larger prostate volumes (P = .04). Obesity was not significantly related to age (P = .19) or race (P = .37). On univariate analysis, obesity was not associated with prostate cancer risk (odds ratio [OR] 1.13, 95% confidence interval [CI] 0.73-1.75, P = .58). However, after adjusting for multiple clinical characteristics, obesity was associated with significantly increased prostate cancer risk (OR 1.98, 95% CI 1.17-3.32, P = .01). After multivariable adjustment, there was no significant association between obesity and high-grade disease (P = .18).'] Is obesity a significant risk factor for prostate cancer at the time of biopsy?