Takeuchi T, Ishigaki Y, Hirota Y, et al. - Questionnaires to a total of 1,957 academic councilors or responsible people at certified facilities of the Japan Diabetes Society as well as at the department pediatrics or neonatology in medical centers with > 300 beds was sent intending to conduct a nationwide survey of insulin resistance syndrome (IRS) of type A or B and Rabson-Mendenhall/Donohue syndrome in Japan. A total of 904 responses with data on 23, 30, and ten cases of type A or B IRS and Rabson-Mendenhall/Donohue syndrome, respectively, was received. With five of these cases testing positive for PIK3R1 mutations, eight cases with type A IRS–like clinical peculiarities although without an abnormality of INSR were tentatively characterized as type X IRS. Type A and type X IRS as well as Rabson-Mendenhall/Donohue syndrome were related to low birth weight. In old people, type B IRS was most often diagnosed and was frequently related to concurrent autoimmune conditions and hypoglycemia. Thus, results generated through this first nationwide survey should give epidemiological insight into these rare conditions and inform better healthcare for afflicted individuals.