Background: The genetic susceptibility to IDDM maps to the MHC class II region, thus one approach to investigating the immunopathogenesis of diabetes is to study first degree relatives of affected individuals. Objectives: To detect the inherited relationship between (HLA-DRB1) allels and type one Diabetic mellitus. Methodology: A case-control study was performed on 90 persons, they divided into three group which are diabetic, siblings and control (30 persons in each group), who attended to Al Zahraa Teaching Hospital /Diabetic Center in Al Kut/Iraq between the period of April; 2012 till April; 2013.data was analyzed by using SPSS 16th version. Distribution of HLA-DRB1 loci among the study groups (type 1 Diabetic patients, Siblings and Control group) were performed using MR.SPOT ROBOTING system. Results: results showed that the frequencies of HLA-DRB1*3,*4 {25 (69.4%)} among Diabetic group were Significant (P value = 0.002), in compare to the corresponding frequencies among control group {11 (30.6%)}, in compare to the frequencies of other HLA-DRB1 loci in both Diabetic group and Control group { 15 (34.1%), 29 (65.9%)} respectively. Meanwhile results have showed that there were no Significant (P value = 0.116), in the frequencies of HLA-DRB1*3,*4 {25 (58.1%)} among Diabetic group in compare to the frequencies of HLA-DRB1*3,*4 {18 (41.9%)} among Siblings group, in compare to the frequencies of other HLA-DRB1 loci among Diabetic group and Sibling group {15 (40.5%), 22 (59.5%)} respectively, also results have showed that there were no Significant (P value = 0.104), in the frequencies of HLA-DRB1*3,*4 {18 (62.1%)} among Sibling group in compare to the frequencies of HLA-DRB1*3,*4 {11 (37.9%)} among Control group, in compare to the frequencies of other HLA-DRB1 loci among Sibling group and Control group {22 (43.1%), 29 (56.9%)} respectively. conclusion: In conclusion there were a genetic predisposition of diabetic Siblings for development of Diabetes since, both Diabetic group and Sibling group showing the highest frequencies of HLA-DRB1 *3,*4, in compare to Control group. Recommendation: larger sample group are required to include other allels