The aim of the present study was to investigate a case of hypersensitivity pneumonitis associated with the use of temozolomide in the treatment of gliosarcoma. A 54-yr-old female developed dyspnoea, cough and hypoxia after surgical resection for gliosarcoma and adjuvant radio- and chemotherapy with temozolomide. A high-resolution computed tomography scan of the thorax showed a bilateral ground-glass pattern. Bronchoscopy with bronchoalveolar lavage and lung biopsies was performed. Bronchoalveolar lavage demonstrated significant lymphocytic alveolitis and transbronchial lung biopsies revealed lymphocytic infiltration with foamy macrophages, consistent with hypersensitivity pneumonitis. There was no evidence of other causes, including infections. After withdrawing temozolomide and initiating prednisolone therapy, the patient had no further pulmonary symptoms. To the present authors' knowledge, this is the first definitively described case of temozolomide-associated hypersensitivity pneumonitis.