Over the last several decades, 12 publications (table) and several reviews1-3 have addressed a difficult question to answer: how many people have inclusion body myositis (IBM)? IBM is one of several autoimmune muscle diseases collectively referred to as inflammatory myopathies. Two other forms of inflammatory myopathy, dermatomyositis and polymyositis (PM), were described in the 1880s and 1890s,4,5 but the first clinical case series of IBM was published almost a century later, in 1978,6 more than a decade after the first epidemiologic studies of PM had been published.7 Most patients with IBM had previously been diagnosed as having PM or some other disorder. Because our ability to count depends on our ability to diagnose, counting patients with IBM has been especially difficult over the last 40 years. Advances in IBM awareness and diagnostic tools, especially improvement in physical examination, have been generally assumed to result in better ascertainment and an apparent increasing prevalence of IBM over the last 2 decades.