A 36-year-old man with adult T-cell leukemia gradually improved to the point of complete remission without any anticancer treatment. The patient was referred to our hospital because of the appearance of morphologically abnormal lymphocytes. Thirty percent of the peripheral blood white cells were morphologically abnormal lymphocytes which had lobulated or indented nuclei, and were E rosette-forming and mature T-cell antigen-positive. No hepatosplenomegaly, lymphadenopathy or mediastinal mass was noted. He had a cough with sputum one and a half years before entry. After admission, skin nodules occurred and were diagnosed histologically as non-Hodgkin's lymphoma, diffuse pleomorphic. Serum antibodies against an adult T-cell leukemia-associated antigen were detected at a titer of 1:40. Chest X-ray films, a pulmonary function test, bronchographic examination, bronchoalveolar lavage and transbronchial lung biopsy demonstrated no relationship between the pulmonary symptoms and the adult T-cell leukemia. After treatment with antibiotics and a beclomethasone inhaler, the symptoms decreased, and then the abnormal lymphocytes and skin nodules disappeared. The spontaneous, complete remission has continued for four years.