We describe the case of a 45-year-old man with ankylosing spondylitis being treated with etanercept who presented with a 1 month history of abdominal pain. CT abdomen revealed an ileocaecal mass associated with an abscess, resulting in a laparotomy and right hemi-colectomy. Histology of the resected specimen showed the classical features of Crohn's disease. Etanercept was stopped and he was started on adalimumab. He is currently in clinical remission from both ankylosing spondylitis and Crohn's disease.