[18F]Fluorodeoxyglucose (FDG) positron emission tomography (PET) is increasingly used for the clinical staging of lymphomas and for assessment of response to therapy. We report the case of a woman with classic Hodgkin's lymphoma who had marked FDG uptake by tumor and bone marrow suggestive of diffuse marrow involvement by lymphoma. However, iliac crest bone marrow examination showed marked myeloid hyperplasia without evidence of lymphoma involvement. We discuss the implications for interpretation of FDG-PET imaging of bone marrow in lymphomas.