Objective — to assess the ovarian reserve in patients with recurrent ovarian endometrioid masses, by studying ultrasound and serum markers. Subject and methods. The investigation included 118 patients with ovarian endometriosis. A study group consisted of 78 patients who had undergone surgery for ovarian endometriosis, with ovarian endometrioid masses; a comparison group included 40 patients with new-onset ovarian endometriosis. The ovarian reserve was assessed according to ultrasound criteria and anti-Müllerian hormone (AMH) levels. Results. In the patients with new-onset ovarian endometriosis, the volume of unchanged ovarian tissue was 1.3 times greater than that in the study group patients. Our investigation has established that the patients who had undergone surgery for recurrent ovarian endometrioid masses have a more pronounced statistically significant difference in serum AMH concentrations compared with the baseline values than the patients with new-onset endometriosis: by 1.6±1.2 and 1.2±0.9 ng/ml, respectively. Conclusion. Assessment of the ovarian reserve suggests that the latter is more significantly decreased after surgical treatment in patients with recurrent endometrial masses than in those with new-onset endometriosis. Patients who are to undergo ovarian endometrioid mass re-enucleation should be informed about the potential risk of damage to the follicular reserve and about the need for assisted reproductive technologies.