Background:Crohn disease is a chronic bowel disease that causes serious complications.Prevalence of Crohn disease is increasing.Studies have shown that the behavior of the disease is not stable and severe complications secondary to behavior change over time have been shown.In this study,we aimed to evaluate the prognostic risk factors associated with phenotypic change in Crohn disease in a Turkish patient cohort.Methods:Patients followed up from March 1986 to August 2011 were evaluated for demographic and clinical characteristics to determine possible risk factors and initial clinical phenotype of the disease based on the Montreal classification.The cumulative probabilities of developing stricturing or penetrating intestinal complications were estimated using the Kaplan-Meier analysis.Univariate and multivariate Cox-proportional hazard models were used to assess associations between baseline clinical characteristics and intestinal complications.Results:Three hundred and thirty patients (mean age,30.6 ± 11.1 years;148 female) were included in the study.Mean follow-up duration was 7.4 ± 5.3 years (range:1.0-25.0 years).At baseline 273 patients had inflammatory-type disease,57 patients experienced stricturing/penetrating intestinal complications before or at the time of diagnosis.The cumulative probability of developing complicated disease was 37.4％ at 5 years,54.3 ％ at 10 years,78.8 ％ at 25 years.Independent predictors associated with progression to intestinal complications were current smoking,perianal disease,extra-intestinal manifestations,and location of disease.Conclusions:Location of disease is the most powerful indicator for the development of stenosis and penetrating complications in inflammatory-type disease.Patients with ileal involvement should be considered for more aggressive immunosuppressive therapy.