Summer-type hypersensitivity pneumonitis is a common form of hypersensitivity pneumonitis in Japan in which Trichosporon is the main antigen. The nonfibrotic form is caused by inhalation of large amounts of Trichosporon in dwellings during the hot and humid summer months and is relieved by antigen avoidance. On the other hand, the fibrotic form, which is caused by persistent inhalation of antigen, presents a form similar to idiopathic pulmonary fibrosis and has a poor prognosis with little improvement even with antigen avoidance.