Objective To develop a prognostic model for the outcome of IUI. Desig n Retrosp ective cohort study. Setting Four fertility centers in The Netherlands. Patient( s) Couples of whom the female partners had a regular cycle and who had been trea ted with IUI. Intervention(s) Intrauterine insemination with and without ovarian hyperstimulation. Main outcome measure(s)-Ongoing pregnancy. Result(s) Overall , 3,371 couples were included who underwent 14,968 cycles. There were 1,229 (8.2 %) pregnancies, of which 1,000 (6.7%) pregnancies were ongoing. Logistic regre ssion analysis demonstrated that increasing maternal age, longer duration of sub fertility, presence of male factor subfertility, one-sided tubal pathology, end ometriosis, uterine anomalies, and an increasing number of cycles were unfavorable predictors for an ongoing pregnancy. Cervical factor and the use o f ovarian hyperstimulation were favorable predictors. The area under the receive r operating characteristic curvewas 0.59. When couples were divided into four ca tegories based on prognosis, the difference between the predicted and observed c hance, that is, the calibration, was less than 0.5%in each of the four groups. Conclusion(s) Although our model had a relatively poor discriminative capacity, data on calibration showed that the selected prognostic factors allow distinctio n between couples with a poor prognosis and couples with a good prognosis. After external validation, this model could be of use in patient counseling and clini cal decision making. Objective To develop a prognostic model for the outcome of IUI. Design Retrosp ective cohort study. Setting Four fertility centers in The Netherlands. Patient (s) Couples of whom the female partners had a regular cycle and who had been trea ted with IUI. Intervention (s) Intrauterine insemination with and without ovarian hyperstimulation. Main outcome measure (s) -Ongoing pregnancy. Result (s) Overall, 3,371 couples were included who underwent 14,968 cycles. There were 1,229 (8.2%) pregnancies, of which 1,000 ( 6.7%) pregnancies were ongoing. Logistic regre ssion analysis demonstrated that increasing maternal age, longer duration of sub fertility, presence of male factor subfertility, one-sided tubal pathology, end ometriosis, uterine anomalies, and an increasing number of cycles were unfavorable predictors for an ongoing pregnancy. Cervical factor and the use of ovarian hyperstimulation were favorable predictors. The area under the receive r operating characteristic curve was 0.59. When couples were divided into four ca tegories based on prognosis, the difference between the predicted and observed c hance, that is, the calibration, was less than 0.5% in each of the four groups. discriminative capacity, data on calibration showed that the selected prognostic factors allow distinctio n between couples with a poor prognosis and couples with a good prognosis.