Introduction: Type 1 Diabetes mellitus (DM1) undeniably affects oral health. High glucose levels may be associated with low salivary flow, accumulation of plaque and tooth decay. The objective of this study is to determine the prevalence of caries and Oral Hygiene Index (OHI) in children with DM1 in Maule Region, Chile during 2008. Patients and Method: A cross-sectional study was designed to examine patients under 15 years old with DM1, who were admitted to Talca Regional Hospital. History of caries (decayed, sealed and lost teeth) was registered according to the COPD-dmft index, OHI (> 1.2 high accumulation of plaque) and potential of cariogenic diet (high, medium or low). The statistical relationship between caries history and gender, OHI and diet was analyzed. Results: 25 children cases with DM1 were studied; the prevalence of caries was 92%, which was mostly in boys (p = 0.03) and associated with poor hygiene (p < 0.01). The average COPD- ceod index was 2.96 ± 2.33 and 2 ± 2.64 respectively. The average OHI was 1.8 ± 2.64, 84 % corresponded to bad oral hygiene. 21 children (84 %) had a diet with low cariogenic potential, not associated to the presence of caries (p = 0.17). Conclusion: The children oral health was precarious and it may be associated directly with poor oral hygiene and not with the food consumed.