We report two cases of Churg-Strauss syndrome with impaired prognosis. Case 1: A 58-year-old woman started to complain of progressive dysesthesia and muscle weakness of the lower extremities on February 6, 1992 and was admitted to our hospital eight days later. The eosinophil count was 1, 170/microliters and chest X-ray on admission revealed bilateral diffuse interstitial shadows. Necrosis of muscle fibers and significant infiltration of eosinophils into vessel walls were histopathologically demonstrated. Case 2: A 69-year-old woman was admitted to our hospital with productive cough and back pain. An expiratory wheeze was audible in all lung fields and bronchial asthma was diagnosed. Laboratory findings showed eosinophilia (8, 550/microliters), an IgE level of 16, 266 IU/ml and no positive data for allergic bronchopulmonary aspergillosis. A biopsy of subcutaneous nodules in the lower extremity revealed significant edema of vessel walls and infiltration eosinophils and lymphocytes. Churg-Strauss syndrome was diagnosed in both cases, and corticosteroid therapy was successful in alleviating eosinophilia. However, symptoms of vasculitis in case 1, including mononeuritis multiplex, did not improve, and cardiomyopathy in case 2 progressively worsened. Particularly in elderly patients, it is very important to make an early diagnosis and to initiate therapy that does not disturb quality of life, even for diseases generally regarded as having a good or fair prognosis.