The incidence of monozygotic twinning (MZT) appears to be increasing within the field of assisted reproductive technology (ART), although the factors contributing to the phenomenon are still far from being identified. On the contrary, in vitro maturation (IVM) of oocytes is becoming more accepted and more and more babies have been born worldwide using this procedure. Assessing its safety and impact on monozygotic twinning (MZT), and following up the health of these babies, is essential. We report here a first case of successful monozygotic (MZ) twin delivery following IVM. The patient was a 28-year-old Japanese female, referred to the IVF clinic for primary infertility. Several previous cycles of ovarian stimulation had resulted in ovarian hyperstimulation syndrome (OHSS). The patient received norethisterone-mestranol to initiate the menstruation, and oocyte retrieval was performed 36 h after hCG. A total of 22 immature oocytes were obtained. Following incubation for 24 h in IVM medium, 50% of the oocytes were matured to the metaphase II (MII) stage. Nine oocytes were fertilized after ICSI with the husband's sperm. Three day 3 embryos were transferred into the uterus on the fourth day following oocyte retrieval. Three weeks after embryo transfer, a single gestational sac was visualized in the uterus. At 7 weeks of gestation, two fetal poles with cardiac activity were seen in the single gestational sac. Serial ultrasound examinations revealed a MZ, monochorionic diamniotic pregnancy. After intensive perinatal monitoring, two healthy male infants were delivered by Caesarean section at 35 weeks of gestation.