Objective: To assess the effectiveness of controlled ovarian hyperstimulation (COH) in intrauterine insemination (IUI) for subfertile couples with an abnormal postcoital test and a poor prognosis.Design: Randomized clinical trial.Setting: Twenty-four fertility centers in the Netherlands.Patient(s): Subfertile couples with a well-timed nonprogressive PCT and additional factors that reduce fertility.Intervention(s): Couples were randomly allocated to three cycles of IUI with COH or three cycles of IUI without COH.Main Outcome Measure(s): Ongoing pregnancy within three IUI cycles.Result(s): We randomly allocated 132 couples to IUI with COH, and 133, to IUI without COH. We observed 33 pregnancies (25%) in the couples allocated to IUI with COH, of which 28 were ongoing (21%), vs. 28 pregnancies (21%) in the couples allocated to IUI without COH, of which 23 were ongoing (17%; relative risk of an ongoing pregnancy, 1.2; 95% confidence interval, 0.75 to 2.0). Two multiple pregnancies occurred in the IUI with COH group, and one, in the IUI without COH group.Conclusion(s): In couples with an abnormal PCT and a poor prognosis, IUI with COH leads to pregnancy rates comparable to those for IUI without COH. We propose to perform IUI without COH in couples with an abnormal PCT. (Fertil Steril((R)) 2007;88:1618-24. (c) 2007 by American Society for Reproductive Medicine.).