( Criteria】 Low back pain at least 3 months duration improved by exercise and not relieved by rest 2. Limitation of lumbarspine in sagittal and front planes 3. Chest expansion decreased relative to normal value for age and sex 4. Bilateral sacroiliitis grade 2-4 5. Unilateralsacroiliitis grade 3-4 Definite ankylosing spondylitisif unilateral grade 3 or 4, or bilateral grade 2-4 sacroiliitis and any clinial criterion【 Criteria 】 1. Low back pain at least 3 months’ duration improved by exercise and not relieved by rest 2. Limitation of lumbar spine in sagittal and front planes 3. Chest expansion decreased relative to normal value for age and sex 4. Bilateral sacroiliitis grade 2-4 5. Unilateral sacroiliitis grade 3-4 Definite ankylosing spondylitis if unilateral grade 3 or 4, or bilateral grade 2-4 sacroiliitis and any clinial criterion