Objective: To assess the effect of a sharp increase in estrogen levels on overactive bladder (OAB) symptoms among women undergoing ovulation induction. Methods: 100 consecutive women (mean age 36.9 ± 5.2 years) who underwent IVF treatments, were prospectively enrolled. Three validated questionnaires on urinary urgency, urinary incontinence, and lower urinary tract symptoms were used to evaluate patient's OAB symptoms before ovulation induction (low estradiol level) and prior to ovum pickup (peak estradiol level). Results: Of the 100 women, 49 reported OAB symptoms prior to ovulation induction (mean USIQ severity score 33) and 51 women were asymptomatic. Of the 49 symptomatic women, 44 (90%) remained symptomatic (mean USIQ severity score 34) and 5 women became asymptomatic through ovulation induction. Of the 51 asymptomatic women, 24 (47%) developed de novo OAB symptoms, while 27 women (53%) remained asymptomatic through ovulation induction. The mean peak estradiol level was significantly higher among women who remained asymptomatic in comparison to women with de novo OAB symptoms (2069 versus 1372 pg/ml; respectively). Moreover, in most (63%) women who remained asymptomatic, peak estradiol levels were higher than 1500 pg/ml, whereas in most (67%) women who became symptomatic, peak estradiol levels were lower than 1500 pg/ml. Conclusion: A higher estradiol level appears to have a protective effect against the development of OAB symptoms during ovulation induction. Further, in most (63%) women who remained asymptomatic, peak estradiol levels were higher than 1500 pg/ml. This finding may suggest a threshold for estradiol activity in the lower urinary tract.