The incidence of scar endometriosis in Cesarean sections varies between 0.03 and 0.4%. However, the recently increased rate of Cesarean sections worldwide may be causing an increase in occurrence of scar endometriosis. This report presents anatomopathological evidence of an early-stage malignant transformation in endometriotic tissue from a post-Cesarean scar and briefly reviews possible underlying mechanisms. A 40-year-old woman with a body mass index of 42.7 was referred to the gynecological department with recurrent pain and presence of a palpable mass in her Cesarean section scar. She had undergone this procedure 7 years earlier and began experiencing discomfort and pain at the incision site 6 months postoperatively. Surgical treatment was instituted with complete removal of the lesion. Anatomopathological examination revealed endometriotic tissue intertwined with atypical endometrial hyperplasia and fibrosis. At 2 years' follow-up, she was asymptomatic, both clinically and based on ultrasound examination. Endometriotic foci inoculated within an abdominal scar may undergo malignant transformation. Long-lasting abdominal scar endometriosis, in morbidly obese women, requires special attention from the physician.