Overall body fat and central adiposity may reflect different mechanisms leading to urinary incontinence (UI). We examined the associations of BMI and waist circumference with incident UI, including the independent associations of BMI and waist circumference with UI type, among women aged 54-79 years in the Nurses' Health Study. Study participants reported their height in 1976 and their weight and waist circumference in 2000. From 2000 to 2002, we identified 6,790 women with incident UI at least monthly among 35,754 women reporting no UI in 2000. Type of incontinence was determined on questionnaires sent to cases with at least weekly incontinence. Relative risks (RRs) and 95% confidence intervals (CIs) were estimated using multiple logistic regression. There were highly significant trends of increasing risk of UI with increasing BMI and waist circumference (P for trend <0.001 for both). Multivariable RRs of developing at least monthly UI were 1.66 (95% CI 1.45-1.91) comparing women with a BMI of > or =35 kg/m(2) to women with BMI 21-22.9 kg/m(2) and 1.72 (95% CI 1.53-1.95) comparing women in extreme quintiles of waist circumference. When BMI and waist circumference were included in models simultaneously, BMI was associated with urge and mixed UI (P for trend 0.003 and 0.03, respectively), but not stress UI (P for trend 0.77). Waist circumference was associated only with stress UI (P for trend <0.001). These results suggest that women who avoid high BMI and waist circumference may have a lower risk of UI development.