Abdominal wall endometriosis is rare and its diagnosis is difficult. However, the consequences may be serious, like recurrences or even malignant transformation. We report a rarer case of asymptomatic abdominal wall endometrioma, accidentally found during a surgical procedure for a second cesarean section, in a 39-years old patient, without any relevant history of endometriosis. The tumor was subcutaneous, 3/3 cm in size, located in the left angle of the incision from the 15 years previously performed cesarean section and freely mobile in relation with the skin and the fascia. It was excised, with clear margins (to prevent recurrences), during the procedure. The patient was discharged after five days. The postoperative period and the follow-up at one and three months were uneventful. The pathological examination clarified the diagnosis by revealing an endometrioma with decidual reaction. Such a condition may be, therefore, evoked before an abdominal wall tumor, even without specific symptoms, even in a 39-years old woman and longtime after the possible causal surgery. Pathological examination remains the ultimate diagnostic tool. Relevant prophylactic attitude at the end of the cesarean section may be considered.