Objective. To study the morphological and functional characteristics of the endometrium in patients of reproductive age before and after unilateral adnexectomy using a three-dimensional (3D) ultrasound imaging. Patients and methods. A total of 113 patients after unilateral adnexectomy were examined. The mean age of patients was 32.85 ± 4.01 years. Two patient groups were identified: group 1 (n = 51) consisted of patients with mature teratomas; group 2 (n = 62) included patients who underwent surgery for epithelial ovarian tumors (endometrioid (30; 48.4%), serous (21; 33.9%), and mucinous (11; 17.7%) cystadenomas). The 3D ultrasound examination of pelvic organs was performed in the middle luteal phase of the menstrual cycle before surgery and at 6, 12 months after it. The endometrial thickness, volume, and ultrasound pattern were studied, as well as volumetric vascularity indices: vascularization index (VI), flow index (FI), and the vascularizationflow index (VFI). Based on the ESHRE consensus (2022), the ovarian reserve was assessed. Results. The improvement of endometrial perfusion was noted at 12 months after surgery. In patients with ovarian teratomas, compensatory restoration of morphological and functional properties of the ovary and endometrium was recorded. The opposite pattern was observed in the group of patients with epithelial tumors. Thus, patients operated on for ovarian endometriomas had an extremely thin endometrium (3.5 ± 0.1 mm), whose values were 1.5 times lower compared to those of patients with serous and mucinous cystadenomas; the glandular layer volume was expectedly low (1.1 ± 0.9 cm3). Conclusion. The minimum effective restoration period for the collateral ovary after unilateral adnexectomy is at least 6 months. The qualitative and quantitative parameters of 3D Doppler velocimetry can be used as predictors of the endometrial morphological and functional state in patients of reproductive age. Key words: 3D ultrasound, mature teratomas, cystadenomas, endometrium, endometrioid cysts, VOCAL