Endometriosis, affecting 6%-10% of women of reproductive age, can lead to severe symptoms such as chronic pelvic pain and infertility. Among its rarer manifestations is abdominal wall endometriosis (AWE), which has been increasingly reported following cesarean deliveries. This case discusses a 39-year-old woman who presented with a 13-year history of cyclical pain at her cesarean section scar, exacerbated over the last year by the development of a painful abdominal mass. Medical evaluations indicated endometriosis at the scar, with further investigations including ultrasound and magnetic resonance imaging showing involvement of the rectus abdominis muscle. Elevated tumor markers HE4 and CA-125, along with a biopsy, confirmed adenocarcinoma. The patient underwent extensive surgical treatment, including the resection of the mass, hysterectomy, bilateral salpingo-oophorectomy, and lymphadenectomy. Pathology confirmed moderately differentiated infiltrative adenocarcinoma originating from endometriosis. Despite the absence of postoperative chemotherapy, the patient showed no recurrence, emphasizing the effectiveness of comprehensive surgical management. This case highlights the critical importance of recognizing the potential for malignant transformation in AWE, particularly following cesarean deliveries, and underscores the necessity for vigilant monitoring and personalized treatment strategies. The management of AWE, especially when malignant transformation is suspected, necessitates a multidisciplinary approach similar to that used in ovarian cancer, focusing on rigorous surgical intervention and the potential for adjuvant therapies.© 2024 Japan Society of Obstetrics and Gynecology.