Malignant transformation of endometriosis in the abdominal wall is very rare. Only 50 cases have been described in literature so far. We present a case of a 45-year-old woman with endometrioid cancer, which arose from focal endometriosis in a surgical scar after cesarean section. The time elapsed between cesarean section and the diagnosis of cancer was 22 years. The patient reported to the Clinic of Gynecologic Oncology of the University Hospital in Krakow with a 15-cm abdominal wall tumor located in the region of cesarean section scar. Imaging modalities (abdominal and pelvic computed tomography and ultrasound) showed a solid tumor in the abdominal wall with invasion to abdominal muscles as well as inguinal and external iliac lymph node involvement. Due to the stage of the disease, the patient was put on neoadjuvant chemotherapy. In the light of increasing rates of cesarean section, an increased risk of malignant transformation of endometriosis in the abdominal wall should be considered.