Giannella L1, La Marca A, Ternelli G, Menozzi G. Abstract The abdominal wall is an uncommon site of extrapelvic endometriosis, which usually develops in a previous surgical scar and it should be considered in the differential diagnosis of any abdominal swelling. Endometriosis involving the rectus abdominis muscle is a very rare event and its rarity explains the incomplete nature of the reports in the literature. Up to the present, 18 cases with lesions contained entirely within the rectus abdominis muscle were clearly documented in medical literature with only four cases as a primary location. We report a case, which came to our observation, of primary endometriosis of the rectus abdominis muscle. The patient underwent only surgery without any medical treatment. Currently, the patient is in follow up for four years with no recovery of the disease. In our experience, surgery is the treatment of choice and it is decisive. We reviewed the literature and summarized all reported cases.