Background Dental caries is identified as one of the most prevalent chronic pathologies among the pediatric population on a global scale, constituting a public health problem. Within the permanent dentition, the first molars play a fundamental and critical role both in masticatory functionality and in the development of occlusion and the overall oral health of the patient. Previous research has shown that permanent molars tend to show significantly high levels of caries incidence, and a correlation has been detected between the status of the first permanent molars and the overall caries rate. Objective To investigate the correlation between the overall DMFT index (Decayed, Missing, and Filled Teeth Index in the permanent dentition) and the DMFT calculated from the status of the first permanent molars (FPMs) in a sample of Mexican school-aged children, and to discuss the implications for oral epidemiology. Material and methods A cross-sectional study was conducted on 107 children aged 5 to 12 years at a pediatric dentistry clinic of a public university in Mexico. All data were obtained from medical records. The DMFT index was calculated for the entire dentition, and a separate DMFT index was determined for the first permanent molars. Nonparametric tests were used in the analyses. Analyses were performed in Stata 14 (StataCorp, College Station, USA). Results The mean age was 8.52±1.36 years, and 50.5% were boys. The mean overall DMFT index was 1.90±2.01 and the DMFT-FPM index was 1.71±1.74, a difference of 0.19 (10%) (Wilcoxon: DMFT vs DMFT-FPM, p=0.0009). The correlation between caries indices was very strong (Spearman r=0.9803; p0 and for the DMFT-FPM>0, 57.0%, a difference of 1.9 percentage points (3.2%). The results show an association of experience and caries prevalence by age (p0.05). Conclusions There is a very strong correlation between the overall DMFT index and the DMFT calculated exclusively for the first permanent molars in this sample of Mexican schoolchildren. This suggests that the FPMs contribute significantly to the overall caries experience and could be a key indicator in the diagnosis and monitoring of oral health, taking into account the percentage of underestimation.