Around 20 susceptibility loci for type 1 diabetes mellitus (T1DM) have been mapped. One of these loci, IDDM10, was found on chromosome 10p11-q11. Here, we investigated whether the IDDM10 locus contributes in the susceptibility to T1DM in a Russian family dataset. One hundred and fourteen simplex Russian families, each containing two siblings (one affected with T1DM diagnosed and one nondiabetic sibling), and 97 multiplex families, containing 106 affected full sibling pairs, were studied. Genomic DNA from the venous blood of the patients was genotyped by PCR using 12 microsatellites (D10S193, D10S548, D10S565, D10S586, D10S588, D10S675, D10S1243, D10S1426, D10S1733, D10S1772, D10S1780 and D10S1783) located on chromosome 10p11-q11. Using the multipoint linkage analysis, the region of suggestive linkage, with a multipoint logarithm of odds (LOD) ratio (MLS) value of more than 2.2, was found between markers D10S1733 and D10S1780, an area of 9.0 cM on the genetic map. The maximum linkage peak (MLS = 2.85 and nonparametric logarithm = 2.68) was observed between markers D11S565 and D11S1243. Using the transmission disequilibrium test, an association of these markers, D10S565 (P overall = 0.0082) and D10S1243 (P overall = 0.017), with T1DM was shown. These results suggest the evidence for the IDDM10 susceptibility locus on chromosome 10p11-q11.