Erythema nodosum migrans (subacute nodular migratory panniculitis) is a panniculitis characterized by migrating subcutaneous nodules or plaque on the lower extremity. We describe a 75-year-old woman with idiopathic erythema nodosum migrans which was manifest centrifugally spreading, slightly morpheaform erythematous plaque on the lower left leg successfully treated with indomethacin. She was initially diagnosed and treated as a case with cellulitis and with poor clinical response. A biopsy specimen from this lesion showed that the septal was thickening; fibrous tissue was also seen with lymphohistiocytic infiltrate and occasional multinucleated giant cells with some inflammatory cells infiltrated into the periphery of the fat lobules. Erythema nodosum migrans should be kept in mind in the differential diagnosis of any morpheaform centrifugally expended plaque, especially in the lower extremities in cases of unknown etiology.