Objective: To assess the experience, prevalence, need for treatment and economic impact of caries among students 6-12 years old in four cities in Mexico. Basic research design: Cross-sectional clinical study. Setting: Elementary public schools. Participants: 500 schoolchildren aged 6 to 12 years. Method: Oral clinical examinations using WHO criteria for caries in the primary (dmft) and permanent (DMFT) dentitions. Main outcome measures: Indicators of caries in the primary and permanent dentitions: experience, prevalence, severity and the Significant Caries Index. In addition, we calculated the treatment needs, dental care rate and cost of care. Results: dmft in the primary dentition was 2.59±2.83, and DMFT was 0.82±1.44 in the permanent dentition. Caries prevalence reached 67.7% in the primary and 34.1% in permanent dentition. The treatment needs index was 85.9% and 91.3% in the primary and permanent dentitions, respectively; the dental care index was 13.9% and 8.5%, respectively. The cost of care for caries in the primary dentition was estimated at $22.087 millions of international dollars (PPP US$) when amalgam was the restorative material used, and PPP US$19.107 millions for glass ionomer. For the permanent dentition, the cost was PPP US$7.431 millions when amalgam was used and PPP US$7.985 millions when resin/composite was used as restorative material. Conclusions: The prevalence and experience of caries in the primary dentition were 50% greater than those of other studies carried out in Mexico. In the permanent dentition they were less. There is considerable need for the treatment of caries and minimal experience with restorative care. The cost of care for caries may be assumed to be high for a health system such as Mexico’s. Keywords: Oral health, Dental caries, Child, Mexico, Health Care Costs, Needs Assessment