Evaluate the prevalence and severity of caries in permanent teeth and their association with the treatment needs of 8–12-year-old Mexican schoolchildren. The cross-sectional study was conducted on 1139 8–12-year-old schoolchildren attending two public primary schools in State of Mexico. The study used the International Caries Detection and Assessment System (ICDAS) to examine the prevalence of caries and identify treatment needs in schoolchildren. Other variables considered were age, gender, oral hygiene, dental visits ≤6 months, toothbrushing frequency, and the mother’s years of education. A logistic regression model was used to identify the association between independent variables and treatment needs. In all analyses, two-tailed p values ≤ 0.05 were considered statistically significant. The prevalence of caries lesions was 82.1% (82.2%boys vs. 81.9% girls) considering all lesion categories (ICDAS 1–6), while the distribution of the severity of caries was 17.9% (ICDAS 0), 13.9% (ICDAS 1–2), 28.3%(ICDAS 3–4) and 39.9% (ICDAS 5–6). The treatment needs index was 77.3%. The logistic regression model showed that the schoolchildren with moderate (ICDAS 3–4) and extensive carious (ICDAS 5–6) lesions were, respectively, 61% Odds Ratio ((OR) = 1.61; p = 0.036) and 77% (OR = 1.77; p = 0.013) more likely to present treatment needs. Other variables, such as poor oral hygiene (OR = 1.52; p = 0.009), the mother’s low level of education (OR = 1.53; p = 0.007), and a lack of dental visits (OR = 1.42; p = 0.030) were associated with dental treatment needs. The results obtained show that the 8–12-year-old Mexican schoolchildren presented a high level of treatment needs for moderate and extensive carious lesions (ICDAS 3–6). These findings reiterate the importance of implementing oral health prevention, promotion, and intervention programs to help protect the oral health of school-age children.