Sezary syndrome is a leukemic variant of mycosis fungoides (MF)/cutaneous T-cell lymphoma (CTCL). Bone marrow transplantation (BMT) from a matched unrelated donor was performed in a 22-year-old woman with a 10-year history of Sezary syndrome who had failed treatment with corticosteroids, methotrexate, photochemotherapy, photopheresis, hydroxyurea, interferon-alpha, and cladarabine. At the time of BMT, she had persistent erythrodermic skin disease, adenopathy, circulating Sezary cells and bone marrow (BM) involvement. The patient underwent BMT from a 6/6 HLA-matched unrelated male donor in August 1996. A BM biopsy obtained on day 30 after BMT showed no evidence of lymphoma and complete male donor engraftment. Her skin lesions resolved within 100 days after transplant. Complete staging studies, including T-cell receptor gene rearrangement studies performed at 36 months post-BMT, showed no evidence of recurrent Sezary syndrome. This represents her first durable remission since the initial diagnosis more than 12 years ago. To our knowledge, this is the first patient with refractory Sezary syndrome who has been successfully treated with allogeneic unrelated donor BMT. Our results indicate that this modality may be effective in inducing remission in refractory MF/CTCL, including Sezary syndrome. Biol Blood Marrow Transplant 1999;5(6):400-4.