We report a case of a 59-year-old man who first presented with a nodal diffuse large B-cell lymphoma that later relapsed as an intravascular large B-cell lymphoma. In the initial biopsy specimen, a few intranodal small vessels that contained large lymphoma cells were noted. After 8 months of multiagent chemotherapy, clinical remission was attained. Two years after the initial diagnosis of nodal diffuse large B-cell lymphoma, the patient presented with a rapid onset of multiorgan failure, which at autopsy was shown to be due to intravascular large B-cell lymphoma. Molecular genetic studies showed that these 2 lymphomas had immunoglobulin heavy-chain gene rearrangements that were of identical size, suggesting that they were derived from the same clone. To our knowledge, this is the first report of a nodal large B-cell lymphoma that relapsed as an intravascular large B-cell lymphoma. Although this report is of only a single case, the presence of a relatively inconspicuous intravascular component in an otherwise typical nodal large B-cell lymphoma may be predictive and could affect clinical decisions regarding diagnosis, monitoring, and prognosis of such lymphomas.