Hypersensitivity pneumonitis is an occupational hazard of mushroom workers. We describe a patient with severe hypersensitivity pneumonitis caused by spores of the Shiitake mushroom (Lentinus edodes) who showed a marked decrease in pulmonary perfusion, as demonstrated by pulmonary scintigraphy. This patient was treated successfully with prednisolone. These results suggest that pulmonary vasculitis may be associated with patients with hypersensitivity pneumonitis, and that steroid therapy may be clinically useful in treatment.