Dear Sir, From 1986 to 1994 we screened 2,064 diabetic patients (1,798 with non-insulin-dependent (NIDDM) and 266 with insulindependent diabetes (IDDM)) in the German district of Hesse. In this group we found 38 patients (22 male, 16 female) fulfilling the criteria for MODY (maturity-onset diabetes of the young) established by Tattersall and Fajans [1](diagnosis before the age of 25 years and treated successfully with diet or oral drugs for 5 years). All these patients had at least one first-degree relative with diabetes mellitus. MODY has become particularly interesting to study recently because it may serve as a genetic model for NIDDM, a major metabolic disorder rising in incidence worldwide [2, 3]. In 1981 Panzram and Adolph [4] published the results of a survey of 40,927 East German diabetic patients from whom they had collected a subgroup of 58 MODY patients (0.14%). According to our results MODY seems to be 12.9 times more frequent (1.8% of all diabetic patients) and even 15 times more frequent with regard to the NIDDM group (2.1%). Since such a vast difference in epidemiological data from neighbouring areas of Germany appears to be unlikely, MODY may not be quite so rare as previously estimated. These data appear to be not only important for the epidemiologist but also for the