The aim of this study was to describe and compare findings regarding the prevalence and severity of dental caries when using ICDAS and DMFT/dmft in an epidemiological study with children and their mothers. This cross-sectional study evaluated 150 preschoolers and their mothers. Data were collected with ICDAS and then transformed into DMFT/dmft. ICDAS scores related to caries were analyzed according to three different cut-off-points: CP1 (0-healthy/1-6-caries), CP2 (0-1-healthy/2-6-caries) and CP3 (0-2-healthy/3-6-caries), representing the D/d of DMFT/dmft. ICDAS codes regarding restorations, except sealants, were considered the F/f and the code 97 as the M/m of DMFT/dmft index. Prevalence of caries and its severity with ICDAS were 92%, 84% and 31.3% in children and 97.3%, 96.6% and 80% in adults according to CP1/CP2/CP3, respectively. Admitting CP3 as the standard for data transformation of ICDAS in DMFT/dmft, it was observed that DMFT/dmft index would underestimate 60% of non-cavitated lesions in children and 16.6% in adults. The DMFT/dmft underestimated the presence of disease to disregard non-cavitated lesions for the pediatric population evaluated. The choice of which is the best index for epidemiological surveys will depend on the purpose of the research and the target population: if it is to estimate the needs of the population to determine clinical care in children and adults, the DMFT/dmft may be sufficient. However, if the objective is to have a more comprehensive diagnosis of caries at the population level in order to develop preventive strategies, to halt and reverse the disease, the detection of non-cavitated-lesions becomes important, mainly in young children.