The clinical manifestations of rheumatoid arthritis (RA) and ankylosing spondylitis (AS) differ in many ways. The age of onset in AS is much younger, with an average onset of 28 years compared with 40-50 years in RA, and with a male predominance (3:1) compared with the female predominance in RA. The genetic association with HLA alleles is stronger in AS, with an HLA-B27 antigen in 95% of the patients compared with RA, with 60% HLA DR4 or DR 1 positives. The type and localisation of arthritis is peripheral polyarthritis in RA, especially with involvement of hands and feet, whereas in AS the arthritis is mainly localized in the spine and sacroiliac joints with an oligoarthritis of the larger joints (hips, knees, shoulders). The radiographic signs in RA show bone resorption with erosive changes in contrast with AS where bone formation with vertebral sydesmophytes is present. Extra-articular manifestations can occur in both diseases but again these manifestations differ in the eye (keratoconjuctivitis sicca and scleritis in RA, versus anterior uveitis in AS), heart (pericarditis in RA, conduction disturbances in AS), lungs (pleural lesions or nodules in RA and fibrosis in AS) and gastrointestinal tract (peptic ulcers in RA and colitis in AS).Both diseases respond well to treatment with NSAIDs but DMARDs, which are very important in RA, have limited value in AS. TNF alfa blocking drugs, however, show a high efficacy in both diseases.