Idiopathic granulomatous mastitis (IGM) is a rare benign chronic inflammatory disease. Etiology is unknown, but an autoimmune mechanism is suspected. Erythema nodosum is rare extramammillary manifestation of IGM, and few cases have been reported in the literature. In this study, we presented 28-year-old female patient with IGM associated with erythema nodosum. IGM can be caused by autoimmune mechanism and treated with steroid or surgical treatment.