In the records of the Registrar-General of England and Wales prior to the year 1940, diabetes was accorded by the rules of classification a high preference over other causes mentioned in association with it upon death certificates, the only important causes preferred to it being the infective diseases cancer, rheumatic fever, sequelae of syphilis, injuries, poisoning, acute intestinal obstruction and puerperal sepsis. It was ascertained from a sample of 123,000 deaths during 1921–30 that 91 % of all death certificates with mention of diabetes were classified to diabetes; in other words the death-rates represented 91 % of the total mortality suffered by persons recognized as diabetics and recorded on certificates as such. It is important to keep this fact in mind when seeking explanations for the trends of mortality at different ages between the years 1860 and 1940.