Hypersensitivity pneumonitis (HP) derives from the inhalation of organic and/or inorganic antigens by susceptible individuals. The authors report the case of an eighteen-year-old female, who worked as a tobacco planter in Pelotas, southern Brazil. She had been presenting progressive dyspnea, dry cough, and weight loss for 35 days. She had fine thoracic crepitations and X-ray examination revealed diffuse interstitial infiltration. The diagnosis of HP was determined by her history of exposure to tobacco, tomographic findings and anatomopathologic examination of the lung, obtained by open biopsy. Tobacco antigens were found to be the cause. As patient was treated with prednisone and tobacco exposure was discontinued, a good clinic and functional response was observed.

Keywords: Therapeutics. Extrinsic allergic alveolitis. Tobacco. Diagnosis.