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Appendectomy has been suggested as a possible protective factor in ulcerative colitis and as a risk factor in Crohn's disease. Tonsillectomy has also been associated with Crohn's disease. We performed a case-controlled study to investigate these associations in a homogeneous Greek population.One hundred thirty-four consecutive cases of ulcerative colitis and 76 cases of Crohn's disease were included in the study. For each inflammatory bowel disease patient and a corresponding healthy control subject, matched for gender, age, and educational level, a standard record on various risk factors was completed by interview. The association between disease status and risk factors was assessed by Pearson's chi-squared test and the independent contribution of each risk factor was analyzed by means of logistic regression analysis.Appendectomy had been performed in 11 (8.2 percent) patients with ulcerative colitis, in 18 (13.4 percent) of their matched healthy control cases, in 19 (25.0 percent) patients with Crohn's disease, and in 10 (13.2 percent) of their matched healthy control cases. Odds ratio for development of ulcerative colitis after appendectomy was 0.6 (95 percent confidence interval, 0.26-1.27). Odds ratio for Crohn's disease was 2.2 (95 percent confidence interval, 0.94-5.12). Odds ratio for development of ulcerative colitis or Crohn's disease after tonsillectomy was 0.95 (95 percent confidence interval, 0.49-1.82) and 3.29 (95 percent confidence interval, 1.29-8.37), respectively. The logistic regression analysis showed that appendectomy and tonsillectomy have no independent association with the risk of developing ulcerative colitis, whereas in Crohn's disease both appendectomy and tonsillectomy have positive associations. Wellestablished risk factors, such as family history and smoking status, were also verified in this study.This case-control study, using multivariate logistic regression analysis, showed a less pronounced association between ulcerative colitis and appendectomy than previous reports. Our data also support the conclusion that tonsillectomy is a risk factor for developing Crohn's disease.