ObjectiveTo identify whether the time interval from insemination to ovulation (I-O interval) affects outcome after intrauterine insemination with donor sperm (IUI-D).DesignRetrospective study.SettingA single public medical center.Patient(s)1,165 couples, for 2,091 IUI-D cycles.Main Outcome MeasureLive birth rate (LBR) ResultsMultiple predictors were identified for LBR. The I-O interval was the predictor for LBR. An I-O interval ≥19 hours significantly decreased CPR (odds ratio [OR], 95% confidence interval [CI] =0.285, 0.171-0.475) and LBR (OR, 95%CI =0.322, 0.189-0.549). The presence of at least two follicles ≥18mm on ovulation day significantly increased the LBR (OR, 95%CI =1.274, 1.012-1.602). Women aged 35 years and older had a significant decreased LBR (OR, 95% CI =0.607, 0.377-0.976).Conclusion(s)The I-O interval, a new prognostic factor, combination with the women’s age and number of mature follicle, can predict the outcome after IUI-D. IUI-D is best performed within 19 hours of I-O interval for a higher probability of clinical pregnancy and live birth.