Background <p>Turner syndrome (TS) is a chromosomal disorder caused by complete or partial loss of one X chromosome, resulting in a high risk of premature ovarian insufficiency (POI) and infertility. While the underlying mechanisms are not fully understood, oocyte loss is known to begin in fetal life and continue throughout childhood, often leading to ovarian failure before the onset of puberty. Ovarian tissue cryopreservation (OTC) offers a potential method to preserve fertility in girls with TS, but the procedure remains experimental in this group. To date, only three cases of autotransplantation have been reported, and no live births have occurred in women with TS. Moreover, predictors of residual ovarian function and eligibility for OTC are poorly defined, and the long-term effects of unilateral oophorectomy in girls with already limited ovarian reserve are unknown.</p> Objective <p>To investigate long-term reproductive outcomes following OTC in girls with TS.</p> Methods <p>The Danish Turner Syndrome Cryopreservation Study is a nationwide, prospective cohort study with long-term follow-up, combining observational and interventional elements. Girls with TS aged 2–17 years are invited to participate. As ovarian reserve is depleted before adulthood in most girls with TS, all participants undergo ovarian function assessment to evaluate the likelihood of remaining viable follicles. If follicles are deemed present, unilateral OTC may be offered. The primary outcome is the number of pregnancies, miscarriages, and live births following autotransplantation of cryopreserved and thawed ovarian tissue in adulthood. Secondary objectives include identifying early predictors of POI, assessing the impact of oophorectomy on ovarian function and pubertal progression, and exploring molecular mechanisms of ovarian dysgenesis through genetic and epigenetic analyses of ovarian and peripheral tissues. Recruitment began in January 2024 and is ongoing at three university hospitals across Denmark. Follow-up is expected to continue until 2050.</p> Conclusion <p>This study addresses a critical gap in fertility preservation for girls with TS by evaluating the feasibility and long-term outcomes of OTC. The findings will improve understanding of POI progression, refine selection criteria for OTC, and support evidence-based counselling for girls with TS and their families.</p> Trial registration <p>ClinicalTrials.gov, NCT05740579. Registered 13 February 2023. https//clinicaltrials.gov/study/NCT05740579.</p>