The case of a 20-year-old pregnant woman with a history of one previous cesarean section (CS) who developed a tumorous mass in the area of the CS scar is presented. The clinical diagnosis of endometriosis or fibromatosis was made but the histologic findings were confusing and the pathological diagnosis of an inflammatory type of liposarcoma was made. The case was referred to our Laboratory for re-evaluation and the diagnosis of gossypiboma was made based on histopathological features, the patient's age, her medical history and the exact location of the lesion. Gossypiboma is a foreign body-related inflammatory pseudotumor caused by retained non-resorbable or even resorbable substances, such as glue, surgical gause or sutures. It is an obscure lesion ignored by doctors of all specialties studying the differential diagnosis of a postoperative mass.