Purpose: To evaluate the cumulative incidence and progression of erosive tooth wear (ETW) and identify risk factors over 18 months in a cohort of 11- to 14-year-old schoolchildren in Mexico. Methods: The study was conducted in public schools located in northern Mexico City. Permanent teeth of 424 schoolchildren were examined using the basic erosive wear examination. The possible risk factors were included in the logistic models: the consumption of acidic food and beverages; habits related to the consumption of beverages; medication; gastroesophageal reflux; frequent vomiting; and characteristics of the saliva. Results: The prevalence of ETW was 62.5 percent (265 out of 424). The cumulative incidence was 35.2 percent (56 out of 159) and the progression was 72.8 percent (193 out of 265). The consumption of acidic beverages increased the relative risk (RR) of both the cumulative incidence (RR equals 1.09; 95 percent confidence interval [95% CI] 1.02 to 1.18; P=0.005) and the progression (RR equals 1.16; 95% CI 1.01 to 1.34; P=0.003). Conclusions: This population has a high risk of the development and progression of ETW, found in approximately one-third and approximately two-thirds of the schoolchildren, respectively. The most important risk factor was the consumption of acidic beverages.