Intravascular large B‐cell lymphoma (IVLBCL) remains a diagnostic challenge, because of non‐specific findings on clinical, laboratory, and imaging studies. We present a case in which 18F‐fluorodeoxyglucose (FDG)‐positron emission tomography (PET)/computed tomography was particularly useful to suspect the diagnosis, to detect unexpected locations, to guide contributive biopsy, and to assess the response to treatment. In case of initial negative results, FDG‐PET should be repeated in the course of clinical evolution. In the presence of neurological or hormonal symptoms without brain magnetic resonance imaging abnormality, FDG‐PET brain slices could depict additional pituitary and/or brain hypermetabolisms. We discuss the potential interests of FDG‐PET in IVLBCL by a literature review. Copyright © 2014 John Wiley & Sons, Ltd.