We assessed the impact of lifetime obesity on the development of urinary incontinence (UI). Using data from the Women's Health Initiative, we evaluated the cumulative impact of obesity over a postmenopausal woman's lifetime on the development of UI. Analyses using logistic models assessed the relationship between overweight/obesity duration and the development of UI during the Women's Health Initiative study at year 3. Of the 15,420 women aged 50-79 years, 4,568 (30.0%) developed UI by year 3. When controlling for covariates, the duration of overweight years (OWY) and obese years (OBY) was significantly associated with overall UI. The number of OWY was associated with an increased risk of developing UI postmenopausally (OR 1.17, 95% CI 1.13-1.22) compared to those with 0 OWY. The number of OBY was associated with a higher risk of developing UI postmenopausally (OR 1.28, 95% CI 1.18-1.39). Severity of UI was also associated with higher OWY/OBY. Compared to participants who maintained normal weight, those who gained weight from age 18 to 50 years were more likely to report increased UI (OR 1.26, 95% CI 1.16-1.37), as did those who remained overweight/obese (OR 1.27, 95% CI 1.04-1.55). Those who lost weight reported no difference in rates of any UI. Chronic, increased body mass index status is associated with an elevated risk of UI later in life. Symptom severity also appears to be worsened with duration of increased body mass index status. Weight management should be supported throughout one's lifetime, as it may impact UI in later stages of life.