Human oocyte maturation is considered as the reinitiation and completion of the first meiotic division from the germinal vesicle stage (prophase I) to metaphase II, and the accompanying cytoplasmic maturation for fertilization and early embryonic development. Immature human oocytes obtained from patients undergoing gynaecological surgery, or ovulation induction or having polycystic ovary syndrome (PCOS) can be matured and fertilized in vitro. To date, 80% of immature oocytes matured to metaphase II when cultured in maturation medium supplemented with gonadotrophins and 85% of matured oocytes fertilized and cleaved in vitro. Following transfer of these embryos, pregnancies and live births have been achieved. However, the capacity for oocyte maturation was different when the immature oocytes were retrieved from PCOS patients and when the oocytes were cryopreserved at germinal vesicle stage.