A 76-year-old male was admitted to our hospital because of fever and erythema on the face and extremity. Skin biopsy of the erythematous lesions showed dense neutrophilic infiltrations and diagnosis of Sweet's syndrome was made. Chest computed tomography on admission revealed ground glass opacities in the right upper and lower lung fields. Bronchoalveolar lavage (BAL) showed increased lymphocytes and neutrophils. A search for bacteria, mycobacteia and fungi in BAL fluid was negative. Trans-bronchial lung biopsy revealed intraluminal organization and fibrinous exudates. Neutrophilic infiltrations were scant. These pathological findings were compatible with organizing pneumonia. Bone marrow aspiration was performed because of slight anemia and thrombocytopenia, and a diagnosis of myelodysplastic syndrome was made. Oral prednisone (PSL) of 30 mg/day induced rapid resolution of radiologic and cutaneous lesions and was tapered to 10 mg/day, then radiologic lesions worsened. Steroid pulse therapy followed by PSL 45 mg and immunosuppressive agent resulted in a resolution of his conditions. This case was rare in that organizing pneumonia was associated with Sweet's syndrome.