Hypersensitivity pneumonitis consists of a group of diseases resulting from inhalation of organic particles causing an immunopathological reaction of the lungs in susceptible individuals. The diagnosis requires a detailed and careful history that would include social, environmental, and occupational status, pulmonary function tests, serum precipitins, bronchoalveolar lavage, imaging, and lung biopsy. Early recognition and avoidance of the causative agent is important although the use of corticosteroids hastens improvement of symptoms.