Objective — to identify morphological criteria for incompetence of the lower uterine segment in the area of a postcesarean section uterine scar and to reveal the clinicoanamnestic factors influencing its formation. Subject and methods. A total of 120 pregnant women, including 80 who had a postcesarean section uterine scar, were examined. Group 1 included 39 patients who had signs of uterine scar incompetence as evidenced by morphological examination. Group 2 consisted of 41 patients without obvious myometrial morphological changes; a control group comprised 40 patients who underwent primary cesarean section. Somatic and obstetric/gynecological history data and status were studied in the examinees; objective and morphological examinations of the area of a uterine scar were performed. Results. Histological examination revealed that the following signs of scar incompetence included abnormal connective tissue changes in the scar area; the high degree of disorganization and dissociation of fascicles of smooth muscle cells; the considerable intensity and wide spread of myometrial hydropic dystrophy and isolated smooth myocytes. Combined analysis of clinical and morphological data identified risk groups of women, in whom the probability of postcesarean section scar incompetence was highest. These included a short surgical interval (1—2 years), intra- and postoperative complications after primary cesarean section; immature cervix uteri in full-term pregnancy; and abnormal delivery among the indications for primary cesarean section. Conclusion. When planning a subsequent pregnancy in patients during primary and repeat cesarean section, myometrial biopsy should be carried out for histological examination and evaluation of the lower uterine segment. A point scale to predict uterine scar incompetence has been elaborated on the basis of morphological findings. The authors declare no conflicts of interest.