Experiments in animal models have suggested a role for bacterial overgrowth in the caecum in the pathogenesis of extracolonic inflammation in IBD. The aim of this study was to identify patients with Crohn's disease who have undergone ileocaecal resection and to compare the incidence of new arthritic complications in these patients with those who have never undergone surgery. Patients who had undergone surgery were identified by case note review. The date and nature of surgery were noted. The occurrence of new joint complications (Type 1 and 2 peripheral arthropathy and AS) was noted in patients who had undergone ileocaecal resection and in patients who had never undergone surgery. In the surgery group the timing in relation to surgery was determined. The groups were compared using Kaplan-Meier survival curves and the Logrank test. One hundred sixty-four patients who had undergone ileo-caecal resection and 221 patients who had never undergone surgery for Crohn's disease were studied. The rate of development of arthritic complications in patients presurgery and in the nonsurgical group was identical. However few arthritic complications occurred postoperatively. There were highly significant differences between the nonsurgical group and the postsurgical group (p = 0.0001) and between patients presurgery and postsurgery (p = 0.0006). New arthritic complications are less common in Crohn's disease after resection of the ileocaecal area. This would be consistent with the hypothesis that luminal bacteria in this region are important in the pathogenesis of these complications.