A 36-year-old Caucasian homosexual man was found to have HIV infection on routine screening. He had an eight-year history of chronic diarrhoea, which pre-dated the HIV diagnosis and did not improve after the introduction of combination antiretroviral therapy. After referral to the Gastroenterology department, he underwent fibreoptic colonoscopy. Colonic biopsies revealed the presence of intestinal spirochaetosis. He received a two-week course of metronidazole, which led to complete resolution of his diarrhoea. Intestinal spirochaetosis should be considered in the differential diagnosis of patients with HIV infection and chronic diarrhoea without other apparent cause.