A 69-year-old woman had acquired moderate bronchial asthma at age 62 years that was complicated by sinusitis. She was atopic, with a positive IgE radioallergosorbent test result for house dust mite. At age 67 years, the patient’s asthma deteriorated and she was treated with systemic corticosteroids for several months. By age 68 years, her asthma was under control and she discontinued systemic corticosteroids. In May 2001, at age 69 years, she complained of slight fever, weight loss of approximately 8 kg within 4 months, paresthesia and paralysis of the lower legs and both hands, palpitations, dyspnea, and skin eruption. She had severe motor and sensorimotor neuropathy on both sides of feet and hands (manual muscle test [MMT] score 1 to 3), sinus tachycardia, pulmonary infiltration, purpura, and cardiac tamponade on echocardiography. Laboratory tests revealed a leukocytosis of 20,900/μL, 89.1% of which was eosinophils, and a negative perinuclear anti-neutrophilic cytoplasmic antibody (p-ANCA) result. Cardiac shock developed due to the cardiac tamponade. After she was treated with mechanical ventilation, we examined pericardial biopsies and samples of the pericardial effusion, which revealed extravascular eosinophilic inflammation. CSS was diagnosed in accordance with the criteria of the American College of Rheumatology4–: asthma, eosinophilia (> 10%), paranasal sinusitis, pulmonary infiltrates on chest radiography (may be transient), extravascular eosinophils on biopsy, and mononeuritis multiplex or polyneuropathy. The presence of any four or more of these criteria yields a sensitivity of 85% and a specificity of 99.7% for distinguishing CSS from other vasculitic syndromes. After treatment with corticosteroids and cyclophosphamide, the pericardial effusion decreased and the pulmonary infiltration and skin eruption improved, but the severe motor and sensory neuropathy did not. The patient was treated several times with IV high-dose Ig,5 and the neuropathy improved remarkably to MMT score of 4 to 5.