The nasal peripheral (post-thymic) T-cell lymphoma is an important cause of the midline granuloma syndrome (MGS), in which ulceration and destruction of the tissues of the nose and paranasal sinuses occurs. We reviewed the histology of 9 cases of the MGS treated with radiotherapy, and, using immunocytochemistry, showed 8 cases to be peripheral T-cell lymphomas (PTCL) and 1 a B-cell lymphoma. All patients received radiotherapy and 2 died shortly after treatment from unrelated causes. Two patients with T-cell lymphoma and the solitary case of B-cell lymphoma achieved long-term disease-free survival. The 4 remaining cases of T-cell lymphoma relapsed locally at a median interval of 3.5 months despite megavoltage irradiation of 45-50 Gy (in 3 cases) and inclusion of uninvolved paranasal sinuses and the nasopharynx in the field (in 2 cases). All patients with local relapse achieved, and remain in, remission after treatment with alkylating agents and prednisolone. The disappointing response of some cases of nasal T-cell lymphoma to radiotherapy has been reported by others, and this may be due partly to the heterogeneity of nasal lymphomas. We are unable to provide clear guidelines for treatment but suggest that a role exists for initial treatment with oral alkylating agents and steroids in newly diagnosed cases.