The clinical and radiological features of fourteen patients with Behcet's syndrome have been reviewed with particular reference to joint disease. Thirteen patients (93%) suffered recurrent peripheral oligo- or poly-arthritis, this symptom being the presenting complaint in two (14%). There were no radiographic abnormalities in peripheral joints. Ten patients (71%) complained of low back pain and in seven (50%) there was a mild erosive sacro-iliitis. Five patients (36%) had an enthesopathy (calcaneal spurs) one of whom also demonstrated vertebral body squaring. Patients with sacro-iliitis did not possess the HLA B27 antigen. Behcet's syndrome should be entertained in the radiological differentiation of sacro-iliitis with a clinical arthropathy.