Abstract: Study Objective: Polycystic ovary syndrome (PCOS) is the most common endocrine disorder among people who menstruate. Adolescent and young adult (AYA) military dependents, a large, diverse subset of the United States population, have not been represented in prior reports of PCOS. This study estimated the incidence and prevalence of probable-PCOS (PCOS symptoms in the absence of a documented PCOS diagnosis) and PCOS in AYA military dependents, and described the length of time between probable-PCOS and first documented PCOS diagnosis for people who met both during the surveillance period. Methods: This retrospective cohort study reviewed military electronic medical records and TRICARE insurance claims from the US Military Health System from 2018-2022. We identified female dependents aged 15-21 years with PCOS (International Classification of Diseases, 10th edition (ICD-10); code E28.2x) or possible-PCOS (i.e., having both androgen excess and a amenorrhea or oligomenorrhea ICD-10 code within a 12-month period) who received care through TRICARE due to insurance sponsor’s military service. Results: A total of 8,385 AYA military dependents had PCOS or possible-PCOS. Across the five-year period, the average yearly incidence was 59/10,000 people (range 54-64). The average yearly prevalence was 182/10,000 people (range 159-195) and was lowest among Black (139/10,000 people) and Asian (132/10,000 people) AYA. Conclusion: Rates of PCOS in AYA military dependents are comparable to rates estimated from medical record data in US civilian populations. Identifying barriers to PCOS detection could facilitate earlier treatment access for military dependents.