Approximately 100 years of observation and investigation have demontrated that the terms osteopsathyrosis idiopathica and OI refer to the same disease process. Classically, three cardinal symptoms have been described: bone fragility, blue sclerae and deafness. It is now known that this combination of findings is most likely to appear in patients with the milder form of the disease, and even in this group only some of the patients have all three symptoms. Historically, a hereditary mesenchymal defect transmitted by autosomal dominance has been implicated in the etiology.