The aim of this work was to determine the frequency of caries, periodontal disease and tooth loss in patients affected by diabetes mellitus types 1 and 2. It was a cross-sectional study involving 175 subjects distributed in the following groups: (1) 35 patients with diabetes type 1 (glycosylated hemoglobin values from 6.5%-7%), (2) 35 patients with diabetes type 1 (values of glycosylated hemoglobin higher than 7%), (3) 35 subjects without diabetes mellitus type 1, (4) 35 patients with diabetes type 2 and (5) 35 subjects without diabetes mellitus type 2. The following clinical parameters were evaluated for all the subjects who participated in the study: frequency of caries, filled teeth, missing teeth, prosthetic restoration, bacterial dental plaque, calculus index, probing depth and attachment level. On comparing the groups of patients with diabetes type 1 to the control group, there were no statistically significant differences among any of the study variables. On comparing the group of patients with diabetes type 2 to the control group, there were statistically significant differences in the variables missing teeth (p=0.0134), calculus (p=0.0001), probing depth (p=0.0009) and attachment level (p=0.0093). The variable periodontal disease showed statistically significant dIfferences in the group of patients with diabetes type 2. Prevention, supervision and review of the oral health of patients with diabetes (types 1 and 2) are needed in order to prevent oral alterations.