It is known that immunologic mechanisms play an important role in the disease process of some patients with idiopathic myelofibrosis. Patients with idiopathic myelofibrosis have an increased incidence of autoantibodies and circulating immune complexes. Dermatomyositis is a disorder of unknown cause, but immune-mediated muscle damage is believed to be important as a pathogenic mechanism. We have a patient who had idiopathic myelofibrosis and developed dermatomyositis during the disease course, a previously unreported combination. Increasing clinicians' awareness of both myelofibrosis and dermatomyositis may provide further insight into a possible relationship of the two conditions.