The finding of an abdominal wall nodule in a patient with a history of gynecological or obstetrical surgery, must consider possible endometrioma. The anamnesis and ultrasound are the main elements in the diagnostic hypothesis. Fine needle aspiration cytology can be considered in the preoperative evaluations. The treatment is surgical and consists of a complete resection, with histopathological study to confirm the diagnosis, when the endometrial glands are observed. In order to diminish or avoid recurrence, resection must be performed with wide margins. We present a case of abdominal wall endometrioma in the rectus abdomis muscles, in a patient with caesarean section scar two years before. We review the differential diagnosis in an abdominal wall mass, the diagnostic approach methods and the treatment.