BACKGROUND Intravascular lymphoma (IVL) is a rare lymphoproliferative disorder characterized by the proliferation of large B lymphoma cells within the lumen of small-caliber blood vessels. Clinical features are nonspecific, presenting as a systemic disease with fever and may be life-threatening. Antemortem diagnosis is difficult but may be made with biopsies of affected tissues or with random skin biopsies. CASE REPORT We report the case of a 66-year-old white woman presenting with fever of unknown origin (FUO) who developed neurologic, pulmonary, and hematologic manifestations. The diagnosis of intravascular large B cell lymphoma (IVLBCL) was made by random skin biopsies. She received treatment with steroids, rituximab, cyclophosphamide, vincristine, and doxorubicin (R-CHOP). Her disease evolution was unfavorable and she died after her first cycle of chemotherapy. CONCLUSIONS Our case illustrates that IVL can present as FUO and should be considered in the differential diagnosis of this syndrome, especially in patients with neurologic compromise and persistently elevated serum lactate dehydrogenase. In this case, the diagnosis was made with cutaneous biopsies of visibly unaffected skin. As in our patient, the course of IVL is usually fatal within a few months.