An FDG PET with diagnostic CT was performed on a 52-year-old man for investigation of lymphocytosis and the clinical suspicion of lymphoma. The PET/CT demonstrated diffuse small bowel uptake, prominent mesenteric lymph nodes without significant FDG uptake, and other features suggestive of celiac disease. Subsequently, the patient was found to have markedly elevated celiac disease antibodies (deamidated gliadin IgG and tissue transglutaminase IgA) and to be HLA DQ2 and DQ8 allele positive on genotyping for celiac disease. Gastroscopy and duodenal biopsy also confirmed the diagnosed.