To determine the prevalence, clinical and radiological characteristics of spondyloarthropathy (SpA) in patients with inflammatory bowel disease (IBD), to assess the association between HLA B27 and B51 and the extraintestinal symptoms and to evaluate whether IBD is associated with Behçet's disease (BD). One hundred and sixty-two consecutive adult patients with established diagnosis of IBD as either Crohn's disease (CD) or ulcerative colitis (UC) were evaluated. All the patients including those previously diagnosed with or without SpA had a complete rheumatologic examination and they were evaluated according to the European Spondyloarthropathy Study Group (ESSG) criteria for SpA and The International Study Group for Behçet's disease criteria for BD. The demographic and clinical data were recorded on a standardized form. The radiographies were obtained in all the patients and computed tomography (CT) was performed in the patients with suspected pelvic radiographies and/or low back pain in the physical examination. Radiological evaluation was made according to the Modified New York criteria. HLA B27, B51 and anti-neutrophile cytoplasmic antigen (ANCA) were searched in all the patients. Of the 162 patients with IBD (mean age 41.48+/-11.63 years, male 60, female 102), 78 were CD and 84 were UC. The mean of the IBD duration was 54.92+/-50.32 months and SpA duration was 20.63+/-34.37 months. The prevalence of SpA and AS in IBD was 45.7 and 9.9%, respectively. Frequencies of SpA and AS, the difference between UC and CD were not significant. Spondylitis, enthesitis, peripheral arthritis, oral ulcer and uveitis were not different between UC and CD, but erythema nodosum was found significantly more common in the CD patients compared with UC patients (P=0.005). The duration of IBD and SpA was similar in both groups. As the IBD duration increased, the prevalence of SpA development decreased (rr=0.991, P=0.009). Of the IBD patients, 13.6% were asymptomatic for musculoskeletal manifestations of SpA and their sacroiliac radiographies and CTs showed grade 2 sacroiliitis. HLA B27, B51 and ANCA positivities were not different between the patients with UC and CD. HLA B27 was significantly more common in the patients with sacroiliitis, spondylitis, enthesitis, peripheral arthritis, erythema nodosum, uveitis (P<0.001) and oral ulcer (P=0.025). BD was diagnosed in none of the patients. ANCA positivity was found to be related with the presence of erythema nodosum and uveitis (P=0.001 and P=0.005). The prevalence of SpA and AS is higher in the prospectively evaluated patients with radiological studies than those in the previously published studies. There is a high prevalence of asymptomatic sacroiliitis in IBD. An early diagnosis of inflammatory arthritis in IBD patients may prevent a disability due to SpA and AS.