A 58-year-old man was referred to the internal medicine outpatient department because of abdominal pain and lymphadenopathy. CT imaging revealed multiple mediastinal, para-aortic, mesenteric and pelvic lymphoma. Biopsy of an inguinal lymph node for histology purposes revealed granulomatous lymphadenitis. A watchful waiting approach was adopted. Two and a half years after first presentation, the patient presented with weight loss, fever and night sweats. CT imaging showed progressive lymphadenopathy and hepatosplenomegaly. Histolopathological examination of a laparoscopically removed lymph node showed extensive infiltration with macrophages with stained rod-shaped bacteria (periodic acid-Schiff staining), which is typical of Whipple disease. PCR and biopsies of the small intestine confirmed the diagnosis. Antibiotic therapy was started with rapid clinical and biochemical improvement. A year later PCR of the duodenal biopsies was negative and the antibiotics were discontinued. Whipple disease is a rare chronic infection caused by Tropheryma whipplei. Clinical symptoms can vary, so it often takes a long time to diagnose.