Background and objectives:The aim was to determine the effect of type I diabetes mellitus on eruption time of dentition and to evaluate the dental caries, debris, calculus and gingival index in two groups. Methods: Type I diabetic children and adolescents with age range (6-14) years who were attending to Layla Qasim Center for Diabetes and The Diabetic Child Association Center in Erbil city were included in this study from December 2010 to March 2011. The dentition of all participants was examined for eruption. Besides, the DMF/dmf index, debris index (DI), gingival index (GI) and calculus index (CI) were evaluated. Data obtained from each group were compared statistically. Results: When compared to the non-diabetic group, we observed that dental development was as early as (1.6) years in diabetic group. Results also showed that the total mean value of caries experienced (dmft, dmfs,DMFT and DMFS) by the diabetic group was less than that of the control group with significant differences. The gingival index among diabetic group was higher than the control group. The total mean value of simplified debris index in control group was higher than the diabetic group. In contrast, simplified calculus index was less in diabetic group with a significant difference between them. Conclusion:The findings showed that patients with type I diabetes mellitus had an earlier tooth eruption and plays an important part in the oral health of children.