Encouraged by preliminary phase 1 studies of aerosolized granulocyte-macrophage colony-stimulating factor (GM-CSF, sargramostim) in the treatment of patients with melanoma and other malignancies, we treated a 72-year-old patient with Sézary syndrome, using alternate-week cycles of aerosolized GM-CSF in combination with monthly cycles of extracorporeal photopheresis (ECP). Sézary syndrome, one of the more aggressive forms of cutaneous T-cell lymphoma, is a devastating and highly symptomatic form of non-Hodgkin lymphoma in which malignant clones of mature helper CD4 T cells, containing large, convoluted nuclei known as Sézary cells, circulate in the blood and infiltrate skin. Extracorporeal photopheresis, an immunomodulatory therapy, has become a primary treatment for patients with Sézary syndrome. This pheresis-based therapy combines psoralen and ultraviolet A radiation as systemic photochemotherapy to induce immune responses. However, the activity and efficacy of ECP vary considerably. To our knowledge this is the first patient with Sézary syndrome treated with adjuvant aerosolized GM-CSF combined with ECP. It produced clinical improvement and decreased the number of circulating Sézary cells in a previously ECP-refractory patient.