Inflammation may play a role in the development of benign prostatic hyperplasia and/or lower urinary tract symptoms (LUTS). Higher levels of C-reactive protein (CRP) may therefore be associated with the development of these outcomes. The authors examined the association of CRP levels measured in 1996 with rapid increases in prostate volume, prostate-specific antigen levels, and LUTS as well as rapid decreases in peak flow rates (through 2005) in a population-based cohort of men residing in Olmsted County, Minnesota. Men with CRP levels of > or =3.0 mg/L were more likely to have rapid increases in irritative LUTS (odds ratio (OR) = 2.14, 95% confidence interval (CI): 1.18, 3.85) and rapid decreases in peak flow rates (OR = 2.54, 95% CI: 1.09, 5.92) compared with men with CRP levels of <3.0 mg/L. CRP levels were not significantly associated with rapid increases in prostate volume, obstructive LUTS, or prostate-specific antigen levels. Associations were attenuated after adjusting for age, body mass index, hypertension, and smoking history (irritative LUTS: OR = 2.00, 95% CI: 1.04, 3.82; peak flow rate: OR = 2.45, 95% CI: 0.73, 8.25). These results suggest that rapid increases in irritative LUTS and rapid decreases in peak flow rates may be due to inflammatory processes.