Most cases of intravascular large cell lymphoma are of B-cell phenotype, with a few cases of T-cell lineage and rare cases with histiocytic features described. A definitive natural killer (NK) cell variant has not been recognized. This report is the first to describe the clinical, histologic, immunophenotypic, and molecular features of 2 cases of intravascular lymphoma with an NK cell phenotype (CD3epsilon+, CD2+, CD7+, CD56+, T-cell intracytoplasmic antigen-1+, perforin+, granzyme B+, CD20-, CD4-, CD5-, CD8-, T-cell receptor [TCR]betaF1-). Molecular studies for TCR gene rearrangements revealed a germline configuration. A 41-year-old man had erythematous plaque-like subcutaneous lesions of the lower extremities in which biopsy revealed Epstein-Barr virus-positive intravascular lymphoma. Following chemotherapy and stem cell transplantation, he was alive with no evidence of disease at 1 year. A 47-year-old woman had myalgias, arthralgias, weakness, fever, altered mental status, and pancytopenia. Bone marrow biopsy demonstrated intravascular lymphoma. Therapy was initiated; however, her condition deteriorated rapidly, and she died. Autopsy revealed involvement of multiple organs, including brain, kidneys, ovaries, and bone marrow. These cases represent the first documented examples of an NK cell variant of intravascular lymphoma.