Abstract: INTRODUCTION: BD has been reported to be associated with ankylosing .spondylitis (AS) in many cases. We observed spondyloarthropathy (SpA) in our Behcet's patients more than in the normal population of Iran which is 0.18% (p<0.002). We compared the BD patients having SpA with BD patients not having SpA (control patients). MATERIALS AND METHODS: We found 50 SpA in our 3740 BD patients. Among them, 45 patients met the European Spondyloarthropathy Study Group (ESSG) criteria and 29 patients the New York criteria. Sex, pattern of presentation, symptoms and signs and laboratory findings were compared between SpA and control patients by the chi square test. RESULTS: The prevalence of SpA in Behce's patients was 1.3% (CI=0.4). The mean age at the onset of the disease was 23.5 years (SD= 10.1) for SpA and 26.2 years (SD=9.7) for controls. The difference was significant (p=0.05). Males were 58% (CI=13.7) in the SpA group and 53.7% (CI=1.7) in controls. The comparison of symptoms and signs showed no significant difference for mucous membrane, skin, neuroIogic, pulmonary, and cardiac manifestations in the two groups. Ocular lesions were the same in both groups except for anterior uveitis (60% in SpA, CI=13.6, and 43% in controls, CI=1.6, p<0.02). Joint manifestations were seen in 94% (CI=6.6) of SpA and 37.6% (CI=1.6) of controls (p<0.00001). In SpA joint manifestations were as peripheral joint involvement in 44% (CI=14.5), enthesopathy in 53% (CI=14.6), buttock pain in 13% (CI=9.9), and low back pain in 44% (CI= 14.5). Gastro intestinal manifestations were the same except for the diarrhea that existed in 10%(CI=8.3) of SpA group and in 1.8% (CI=0.4) of controls (p<0.0002). No aneurysm or large vein thrombosis was seen in the SpA group, in opposite of the control group. However, the difference was not significant. The comparison of laboratory findings showed no significant difference for the pathergy test, HLA-B5, and VDRL. The difference for HLA-B27 was significant: 46% (CI= 14.1) in SpA group and 9.5% (CI=1) in controls (p<0.00001). ESR in the range of 20-40, and superior to 100, was the same in both groups: The difference was significant for the range of 50-100 (30% in SpA, CI=12.7, 16% in controls, CI=1.2, p<0.007). CONCLUSION: Our study showed that SpA is more frequent in BD than in normal population. Anterior uveitis, joint manifestations, diarrhea, HLA-B27, and the elevation of ESR were more frequent in the SpA group. There was no large vessels involvement in the SpA group.