We describe a 43-year-old woman who presented a sudden onset of fever and migratory arthralgias. Physical examination revealed tender, well-demarcated erythematous papules and plaques, consistent with a Sweet syndrome. After developing systemic symptoms with hepatomegaly, a liver biopsy and FDG PET imaging demonstrated the presence of an aggressive and extended non-Hodgkin T-cell lymphoma. This case highlights the usefulness of FDG PET imaging for the screening of this paraneoplastic syndrome.