The first wave of the "German Health Interview and Examination Survey for Adults" (DEGS1, 2008-2011) allows for up-to-date, representative prevalence estimates of known diabetes amongst the 18- to 79-year-old resident population of Germany. Temporal trends can be shown by comparing the survey findings with those of the "German National Health Interview and Examination Survey 1998" (GNHIES98). The definition of known diabetes was based on self-reports in physician-administered interviews that asked respondents if they had ever been diagnosed with diabetes by a doctor or were on anti-diabetic medication. Overall, diabetes had been diagnosed in 7.2 % of the adults (7.4 % of the women; 7.0 % of the men). The prevalence increased substantially with advancing age and was higher in persons of low than of high socioeconomic status. Prevalence varied depending on the type of health insurance held and was highest amongst those insured with AOK health insurance funds. In comparison with GNHIES98, there was a 38 % increase in prevalence, of which approximately one third is to be attributed to demographic ageing. In the context of other nationwide studies, the results indicate a figure of at least 4.6 million 18- to 79-year-olds having been diagnosed with diabetes at some point. Planned analyses of undiagnosed diabetes will contribute to the interpretation of the observed increase in the prevalence of known diabetes. An English full-text version of this article is available at SpringerLink as supplemental.