Ovulatory dysfunction is the commonest cause of female infertility. Here we show that the co-repressor nuclear-receptor-interacting protein 1 (Nrip1; encoded by the gene Nrip1) is essential for ovulation. Mice null for this protein are viable, but female mice are infertile because of complete failure of mature follicles to release the oocyte at ovulation. In contrast, luteinization proceeds normally, resulting in a phenotype closely resembling that of luteinized unruptured follicle syndrome, often associated with infertility in women. Therefore, whereas the pre-ovulatory surge of luteinizing hormone induces both ovulation and luteinization, the ability to suppress the action of nuclear receptors is essential for the coordinated control of ovarian function with the essential process of oocyte release dependent on the activity of the transcriptional co-repressor Nrip1 (RIP40).