Discovering the genetic variants associated with ovarian response to gonadotropins is an important step towards individualized pharmacogenetic protocols of ovarian stimulation. More than 90% of the genetic variability is caused by the presence of single nucleotide polymorphisms (SNPs). Pharmacogenetics is the science that describes the relationship between genetic variability and drug response and studies how to tailor pharmacological therapy to the genetic features of the individual patient and how to improve desired actions and minimize side effects. Different genes have been studied in relation to the characteristics of the normal ovarian cycle or different individual responses to controlled ovarian hyperstimulation (COH). The follicle stimulating hormone receptor gene (FSHR) is crucial in follicular maturation: inactivating FSHR mutations almost always leads to amenorrhea and activating mutations can cause a spontaneous ovarian hyperstimulation syndrome or predispose to iatrogenic ovarian hyperstimulation syndrome (OHSS).