Between 1971 and 1978 at St Mark's Hospital and St Bartholomew's Hospital, 8 patients were seen with a psoas abscess complicating Crohn's disease. All patients had a long history of disease and the diagnosis was usually obvious on clinical grounds. The abscess was drained in all patients and 5 required drainage on more than one occasion. The underlying Crohn's disease was treated surgically in all patients. Seven patients are now well, although 2 have required further excisional surgery; 1 patient died 2-years after the first drainage of the psoas abscess.