Purpose.The aim of this article was to report the prevalence of refractive errors, mainly myopia, among 12- to 13-year-old children in a metropolitan setting in Mexico.Methods.A total of 1035 schoolchildren were examined in a field study in Monterrey, Mexico. The examination included best-corrected visual acuity and refraction during cycloplegia. A sample of the children was sent to a pediatric eye clinic and underwent cycloplegic refraction with an autorefractor.Results.We found a prevalence of myopia (≥−0.5 D SE) of 44%, whereas bilateral myopia was present in 37% of the children. In the total sample, high myopia (≥−5D) was found in 1.4%. The prevalence of myopia was significantly higher in girls. Only 20% of children with bilateral myopia used prescription glasses; 8% had prescribed glasses, but did not use them. Hyperopia (≥+1 D) was present in 6.0% of the total population, and astigmatism (≥−1.5 D) was present in 9.5%.Conclusions.The prevalence of myopia among 12- to 13-year-old children in Mexico is high. The majority of cases are low grade, and a large number of the myopic children do not have, or do not use, prescription glasses.