Objective: To develop a prognostic model for the prediction of ongoing pregnancy after single-embryo transfer (SET) following mild stimulation for IVF in women less than 38 years of age. Design: Prospective cohort study. Setting: Two fertility centers in tertiary referral university hospitals. Patient(s): A total of 152 women with an elective SET following mild ovarian stimulation (cycle day 5 start of 150 IU/day recombinant FSH and late follicular phase GnRH antagonist cotreatment). Intervention(s): Database analysis. Main outcome measure(s): Ongoing pregnancy. Result(s): The ongoing pregnancy rate per elective SET was 28% (42 of 152). In a multivariate logistic regression analysis, body mass index, the total gonadotrophin dose needed, and number of oocytes retrieved were negatively correlated whereas the availability of a top-quality embryo was positively correlated with ongoing pregnancy. The predictive ability of the model assessed by the area under the receiver operating characteristic curve was 0.68. At a probability cut-off level of 0.20 the model showed a sensitivity of 37% and a specificity of 90%. Conclusion(s): The developed prediction model for ongoing pregnancy provides an evidence-based strategy for guidance under which conditions SET may be performed. After external validation, application of the model may help to improve overall singleton pregnancy rates.