The search for a phenotypical classification of Crohn 's disease has begun. Support for this strategy is drawn from classification of other chronic diseases, which should encourage further research. Identification of a phenotype will expedite the search for a corresponding gene. For example, autosomal dominant polycystic kidney disease is a common genetic condition affecting I in 1000 people. It has a characteristic phenotype that includes extra renal manifestations (hepatic and pancreatic cysts, cardiac valvular disease, colonic diverticulum). Recently, an abnormal gene on chromosome 16 was described and should identify most patients at risk of disease development. Alterations in clinical management might include careful observations for development of hypertension before development of renal failure in the identified population at risk (4).