© 2016 by American Society of Clinical Oncology. Purpose: Female survivors of childhood, adolescent, and young adult (CAYA) cancer who were treated with alkylating agents and/or radiation, with potential exposure of the ovaries, have an increased risk of premature ovarian insufficiency (POI). Clinical practice guidelines can facilitate these survivors' access to optimal treatment of late effects that may improve health and quality of survival; however, surveillance recommendations vary among the existing long-term follow-up guidelines, which impedes the implementation of screening. Patients and Methods: The present guideline was developed by using an evidence-based approach and summarizes harmonized POI surveillance recommendations for female survivors of CAYA cancer who were diagnosed at age < 25 years. The recommendations were formulated by an international multidisciplinary panel and graded according to the strength of the evidence and the potential benefit gained from early detection and intervention. The harmonized POI surveillance recommendations were developed by using a transparent process and are intended to facilitate care for survivors of CAYA cancer. Results and Conclusion: The harmonized set of POI surveillance recommendations is intended to be scientifically rigorous, to positively influence health outcomes, and to facilitate the care for female survivors of CAYA cancer.