Purpose: To determine the prevalence of myopia in school children in Greater Beijing. Methods: The Beijing Childhood Eye Study was a school-based cross-sectional study. One school of each level (primary, junior high, senior high) was randomly selected from nine randomly selected districts of Greater Beijing. The children underwent non-cycloplegic refractometry and their parents an interview. Results: Of 16 771 eligible students, 15 066 (89.8%) children with a mean age of 13.2 +/- 3.4 years (range: 7-18 years) participated. Prevalence of myopia defined as refractive error of <= -0.50 diopters (D), <= -1.00 D, <= -6.00 D and <= -8.00 D in the right eye was 64.9 +/- 0.4%, 53.0 +/- 0.4%, 4.3 +/- 0.2% and 1.0 +/- 0.1% respectively. In multivariate analysis, prevalence of myopia was significantly (p < 0.001) associated with higher age, female gender, urban region and school type. Prevalence of myopia of <= -1.00 D and of <= -8.0 D increased from 9.7% and 0% in 7 year olds, respectively, to 74.2% and 1.8% in 17- or 18 year olds respectively. The latter figure was already similar (p = 0.39) to the prevalence of high myopia in the elderly Beijing Eye Study population (1.6%). In a subset of 1082 children undergoing cycloplegia, difference in refractive error between prior to and after cycloplegia was 0.31 +/- 0.47 diopters. Conclusions: On the basis of previous investigations from China, our study indicated an ongoing myopic shift in the young generation. Since the prevalence of high myopia in children aged 17 or 18 years was already similar to the one in the elderly Beijing population, the data prognosticate an increase in vision threatening high myopia in the future adult population.