To analyze whether a correlation exists between the caries status (Decayed, Missing and Filled Teeth, DMFT Index) of the first permanent molars (FPMs) and that of the full permanent dentition of Mexican adolescents, and to propose its use in large epidemiological studies of dental caries.We conducted a cross-sectional study of 1538 adolescents from 12 to 15 years old. Based on a clinical oral examination, we determined the DMFT Indices of their FPMs (FPM-DMFT) and of their full permanent dentition (comprehensive DMFT Index). We explored each FPM to determine whether it was with or without caries, filled, missing or sealed. For our statistical analysis, we used Fisher exact test and Spearman correlation in Stata software.After examining a total of 6157 FPMs, we found that 56.8% of our sample of adolescents had no caries in their 4 FPMs whereas 4.9% experienced caries in all 4. No significant differences emerged by sex (P > .05); however, by age, the older adolescents experienced greater FPM-DMFT (P < .05). Analysis yielded a correlation of r = 0.8693 between the FPM-DMFT and comprehensive DMFT scores (P < .0001) of participants. The underestimation of caries prevalence (DMFT > 0) was 5.4% (48.6% vs 43.2%), while the DMFT Index was underestimated at 0.34 (1.15 vs 0.81).The strong correlation between the FPM-DMFT and comprehensive DMFT Indices suggests that overall caries status can be inferred on the basis of FPM caries status. This evidence is useful when conducting large epidemiological studies such as national surveys.