Editor,—In his leading article (Gut1998;43:303–8), Mr Phillips makes a plea for realistic comparisons between outcomes for pouch surgery in Crohn’s disease with other restorative procedures for this disease, rather than comparisons with restorative proctocolectomy for other diseases, specifically ulcerative colitis. We agree that like comparisons are important in scientific analysis, but point out that such comparisons are confounded by the difficulties of accurate histological diagnosis in inflammatory bowel disease. In particular we should like to highlight the diagnostic confusion and unreliability of a change in diagnosis from ulcerative colitis to Crohn’s disease based on the histological examination of the defunctioned rectum in ulcerative colitis.1 Nearly all of the inflammatory changes of Crohn’s disease have been described in the defunctioned colorectum in ulcerative colitis.2 Any change from a diagnosis of ulcerative colitis to Crohn’s disease must be based on a re-examination of the colectomy specimen and placed in context with the clinical history. The misdiagnosis of diverted ulcerative colitis, as Crohn’s disease, will only add further to the confusion surrounding the debate on the role of the pelvic ileal reservoir in Crohn’s disease.