The treatment of chronic diseases is of eminent importance in primary care, and type 2-diabetes mellitus is one of the most common dysfunctions. Its world-wide prevalence has been increasing from year to year. Thus, to estimate the prevalence and incidence of diabetes mellitus, we performed the SESAM (Sächsiche epidemiologische Studie in der Allgemeinmedizin) 2-study in cooperation with general practitioners (GPs) from the German state of Saxony; 270 of the 2510 (10.8%) solicited physicians participated. Cross-sectional data were collected from 1 October 1999 until 30 September 2000, from randomly selected patients previously known to the practitioner. From a total of 8877 consultations with 270 GPs, diabetes was prevalent in 14% (n = 1241) of the patients and the incidence was 0.3% (27 of 8877 cases). The consultation prevalence was estimated at 14.3% (n = 1268; CI 13.6-15%). Of the diabetic patients, 3.5% (n = 44) suffered from type 1-diabetes, while type 2-diabetes was found in 66.9% (n = 848) of the cases. "Other diabetes" was determined in 19.2% (n = 244), and "not further specified diabetes", in 10.4% (n = 132) of the cases. Related to the German population in general, the prevalence ranged from 7.9 to 9.2%. The estimated consultation prevalence is about four times higher than that in other European countries. These data are of importance in illustrating the epidemiology of diabetes in the population and the direct repercussions for GPs. They also point out the significance of diabetes as a major challenge to the German health care system.