Pubertal status at time of fertility preservation in transgender girls

•Puberty blockade and gender affirming hormone therapy can impair gonadal histology that may cause infertility or biological sterility.•The documented rates of fertility preservation among transgender and gender-diverse youth (TGD) remain low.•Spermarche has been reported to occur as early as Tanner 3.•In our study, a sperm sample was successfully produced in a transgender girl at Tanner stage 3 and testicular volume of 12 ml before the development of facial hair or laryngeal prominence.•Early counseling and an interdisciplinary team are vital in maximizing the chances that a patient will be successful in fertility preservation.