The lymph node lesions in Still's disease can be histologically divided into four major categories: 1) simple atypical paracortical hyperplasia, 2) burnt-out histiocytic pattern, 3) exuberant immunoblastic reaction in paracortical hyperplasia and 4) follicular hyperplasia. The second and the third pattern may closely resemble malignant lymphoma. Extended and careful clinical examination with relevant laboratory findings and possible complex histochemical and molecular analysis are necesarry to rule out the suspition of lymphoma. Objective: Intravascular large B-cell lymphoma (IVLBCL) is a rare form of diffuse large B-cell lymphoma characterized by exclusive or preferential intravascular growth. IVLBCL often goes clinically unrecognized. We report three clinically unsuspected cases of classic variant IVLBCL. Method: Cases diagnosed as IVLBCL were collected from the pathology files of Germans Trias i Pujol Hospital. The diagnosis was reviewed in agreement with WHO 2008 criteria and immunophenotypic and clinical data were gathered. Results: A 71-year-old male and an 87 year-old-male showed neurological symptoms leading to progressive deterioration and death. A 79-year-old female presented with fever of unknown origin and died 2 days after admission. At autopsy there were no gross findings suggestive of a neoplastic process in any instance. Histologic study showed intravascular large B cells with vesicular nuclei involving predominantly the central nervous system in the first two cases and the adrenal glands, liver, and spleen in the third case. Conclusion: The three cases of aggressive, advanced-stage lymphoma herein described illustrate how the clinical diagnosis of IVLBCL remains elusive due to its low frequency and variegated clinical presentation and how the pathologic diagnosis of IVLBCL continues to be highly dependent on autopsy examination.