AbstractEndometriosis of the perineum and vulva is extremely rare, with the most common site being episiotomy scars. We report here a case of spontaneously developing perineal endometriosis successfully treated with local excision. A 39‐year‐old woman was admitted complaining of a painful vulvar lump with cyclic swelling. She had first noticed the mass 7 years before, and it had gradually increased in size. Gynecological examination showed a walnut‐size, painful, subcutaneous mass in the left perineum. Magnetic resonance imaging revealed a multilobular cystic mass with inner hemorrhage, suggesting vulvar endometriosis. The patient was treated by local excision of the vulvar mass, and complete excision was achieved. The pathological diagnosis of the excised tissue was endometriosis. The patient is well without evidence of disease 5 months following the local excision. Spontaneous perineal and vulvar endometriosis is extremely rare. However, any lesion that evolves in response to the menstrual cycle should be considered endometriosis.