We report a case of a rectus abdominis muscle endometriotic mass in a woman affected by multiple sclerosis. The pathogenesis of endometriosis is poorly understood but an immune system alteration could play a role in its onset and development. To date few studies have investigated the connection between autoimmune diseases and endometriosis. Multiple sclerosis is an inflammatory, autoimmune, demyelinating disease of the central nervous system. An autoimmune background might contribute both in the establishment of extrapelvic endometriotic lesions and in the possible increased risk of women with endometriosis to develop autoimmune diseases.