<b>Aims</b>: To assess the prevalence of the major oral diseases and the impact of the risk factors in adolescents from three different countries representative of Europe, Latin America and Middle East: Italy, Mexico and Saudi Arabia.<br/> <b>Methods</b>: Caries (ICDAS and DMFS), erosion (BEWE), gingival status (Silness-Löe Index) were recorded. Body Mass Index (BMI) was calculated (WHO guidelines). A questionnaire investigated dietary patterns, oral habits and socio-economic status. Sweet taste evaluation was performed to determine threshold (TT) and preference (TP).<br/> <b>Results</b>: 909 subjects (Italy n= 220; Saudi n=225; Mexico Urban n=224; Mexico rural n=240). Mean DMFS was 2.96 SD 4.01. The prevalence of erosion was higher in Mexico (18.7%), followed by Italy (12,7%) and Saudi (6.7%) while caries experience was higher in Saudi (3.0±4.0), followed by Italy (1.4±2.3) and Mexico (1.2±1.5)(p&lt;0.001). The frequency of soft drinks intake was a constant variable for erosion (p&lt;0.01). Overweight (BMI) was positively related to caries severity. TP and caries had a significant correlation (p&lt;0.01). Subjects in the rural area presented less caries (p&lt;0.01).<br/> <b>Conclusions</b>: The distribution of oral diseases is related to behavioral, socio-cultural and geographic situations. Both caries and dental erosion are associated to diet and diet being determinant to BMI is decisive in oral and general health where prevention can make a decisive change in the quality of life.