After studying 10 cases, we describe a form of late onset, B27 related disease. The patients were men over 50 with minimal involvement of the axial skeleton, mild oligoarthritis of the lower limbs, paucicellular joint fluids and fibrosis on synovial biopsy. In contrast, they appeared severely ill with erythrocyte sedimentation rates elevated and a large amount of pitting edema. Their response to nonsteroidal antiinflammatory drugs was poor. The disease did not abate for from one to several years. Five patients later presented bilateral sacroiliitis and 4 of these developed ankylosing spondylitis (AS). This clinical presentation of AS may owe its distinctive features to its late onsets.