A 57-year-old woman was admitted to our hospital because of cough and low-grade fever for 2 months and shortness of breath for 2 weeks. She had raised two budgerigars for the last 15 years and had been using a feather duvet for one year. A chest radiograph showed diffuse ground-glass opacities in both lung fields, and a chest CT scan showed centrilobular micronodules and ground-glass opacities. Bronchoalveolar lavage (BAL) revealed a marked increase in lymphocytes, and a transbronchial lung biopsy (TBLB) specimen showed alveolitis due to the infiltration of mononuclear cells. Since she had specific antibodies against pigeon and budgerigar dropping extracts and her peripheral blood lymphocytes proliferated on addition of pigeon serum, she was diagnosed as having bird fancier's lung (BFL). She was treated with steroids, which brought about a marked improvement. After she visited her husband who had been hospitalized where a feather duvet was provided for each patient, both subjective and objective findings deteriorated. This deterioration was preventable when she wore a protective mask for micro-dust while visiting her husband. The feather duvets seemed to induce acute BFL in this case, though raising budgerigars may well be related to her sensitization with bird-related antigens.