Abstract: The sensitivity of diagnostic criteria for BD in patients from the United States (US) is unknown. We compared the sensitivity of the 6 major diagnostic criteria in 164 consecutive US Behcet patients diagnosed clinically over a 12 year period. Patients were not prospectively evaluated and pathergy testing was carried out in only 27 of these patients. The sensitivity of these criteria was evaluated in the entire group, in the 27 patients who had pathergy testing and in the group of 137 patients who were not formally tested. In the total group, the Classification Tree was the most sensitive (91.5% ± 4.3) and the International Study Group criteria were the least sensitive (75.6% +6.6), p= 0.001. We found no statistical difference in the sensitivity of any criteria when applied to patients who have or have not had formal pathergy testing when compared with the Chi square test (with the Yates correction). However, because the number of patients in the group having the pathergy test was small, the inclusion and analysis of additional patients tested for pathergy will allow more confident comparisons. The specificity and the accuracy of each set of criteria for both groups will require comparison to control patients. The Classification Tree was the most sensitive criteria (91.2% ± 4.7) for the classification of Behcet patients from the United States who were not tested for pathergy. These criteria were significantly more sensitive than the International Study Group criteria (74.5% ± 7.3, p<0.003), the criteria of Mason and Barnes (78.8% ± 6.8, p<0.004), and the Dilsen criteria (82.5% ± 6.4, p<0.04). The Classification Tree may be the most appropriate criteria for classification of patients with Behcet's disease in the US and for retrospective studies in which patients were not systematically tested for pathergy.