In a 45-year-old man with diarrhoea, upper abdominal pain and malabsorption Whipple's disease was diagnosed by gastroduodenoscopy with small bowel biopsies. The disease is rare and can present with gastrointestinal problems but also with cardiac or neurological complaints. Tropheryma whippelii, the aetiological organism, can be demonstrated by pathological investigation of biopsies and with the polymerase chain reaction (PCR). Treatment with trimethoprim-sulfamethoxazole 160-800 mg twice daily is the therapy of choice: it must be continued for a year, otherwise there is a high possibility of relapse. Correct diagnosis, based mostly on gastroduodenoscopy, can lead to the right therapy and recovery of the patient.