OBJECTIVE: We aimed to evaluate uterine volume and endometrial thickness during the early follicular phase in patients with polycystic ovary syndrome (PCOS) and healthy controls.METHODS: We studied 1,016 PCOS patients and 182 healthy controls. The anthropometric, endocrine, and metabolic characteristics of PCOS were determined. Uterine volume and endometrial thickness were also recorded.RESULTS: Uterine volume progressively increased with age both in PCOS patients and controls. Patients with PCOS and body mass index (BMI) ≥25 kg/m2 had greater uterine volumes than PCOS patients with BMI <25 kg/m2 (P<.001). Patients with the classic PCOS phenotypes (i.e., with oligo-ovulation and/or anovulation [ANOV] and hyperandrogenemia [HA] with or without polycystic ovaries [PCO]) had smaller uterine volume than PCOS patients with the additional phenotypes introduced by the Rotterdam criteria (i.e., with PCO and either ANOV or HA; P = .033) and controls (P = .045).CONCLUSION: Uterine volume increases progressively with age and obesity in PCOS patients. The smaller uterine volumes and endometrial thicknesses in the classic PCOS phenotypes might be attributed to the more severe HA of these patients.