Currently available U.S. population-based data for ankylosing spondylitis (AS), spondyloarthritis and inflammatory back pain (IBP) from the nationally representative U.S. National Health and Nutrition Examination Survey (NHANES) include both NHANES I (1971-1975) and NHANES II (1976-1980) surveys. The pelvic radiographs obtained in NHANES I provided U.S. prevalence estimates for radiographic sacroiliitis, an important component of the AS case definition. AS and spondyloarthritis prevalences cannot readily be calculated from NHANES I survey data; however, IBP prevalence (Rudwaleit et al Criteria 7b) can be estimated from NHANES II. The NHANES II estimate for IBP is 0.8% of the adult population ages 25 to 49 years. The prevalence of IBP in the subset of persons with a history of a back pain episode lasting 2 or more weeks was 6.7%. The 2009-2010 NHANES U.S. Inflammatory Back Pain/Spondyloarthritis survey is currently fielded.