Lymphomas that manifest initially with haemophagocytic syndrome (HPS) often pose a diagnostic challenge, as the majority of cases have no significant lymphadenopathy for early histological diagnosis. There is paucity of data on specific features of fluorine-18-fluorodeoxyglucose (FDG) positron emission tomography with integrated computed tomography (PET/CT) in patients with lymphoma-associated HPS (LHPS). We describe three cases of LHPS and their characteristic PET imaging features. These three patients had pyrexia and pancytopenia. Their PET/CT images showed extensive and diffuse FDG uptakes in the bone marrow of the axial skeleton, with little involvement in the lymph nodes. They also faced a common initial diagnostic difficulty; the lack of nodal involvement on clinical examination or CT contributed to the delay in the diagnosis of lymphoma. The PET/CT images, however, revealed extensive and distinctive FDG uptakes in the axial skeletal marrow compartment, thus leading to a greater appreciation of the full extent of the disease.