PURPOSE. To determine the prevalence and associations of myopia in schoolchildren in provincial Western China. METHODS. In the school-based observational cross-sectional Gobi Desert Children Eye Study, cylcoplegic refractometry as part of a comprehensive ophthalmic examination was performed in all schools in the oasis region of Ejina. Out of 1911 eligible children, 1565 (81.9%) children with a mean age of 11.9 +/- 3.5 years (range, 6-21 years) participated. RESULTS. The mean refractive error in the worse eye was -1.38 +/- 2.04 diopters (D) (median, -0.88 D; range, -13.00 to +6.50 D). In multivariate analysis, more myopic refractive errors were associated with older age (P < 0.001; regression coefficient B: -0.26; 95% confidence interval [CI]: -0.28, -0.23), female sex (P = 0.005; B: -0.26; 95% CI: -0.43, -0.08), more myopic paternal refractive errors (P < 0.001; B: 0.20; 95% CI: 0.14, 0.27), more myopic maternal refractive errors (P < 0.001; B: 0.18; 95% CI: 0.12, 0.24), and fewer hours spent outdoors (P = 0.038; B: 0.18; 95% CI: 0.01, 0.35). The prevalence of myopia, defined as refractive errors (spherical equivalent) of <= 0.50, <= 1.00, and <= 6.00 D in the worse eye, was 60.0 +/- 1.2%, 48.0 +/- 1.3%, and 2.9 +/- 0.4%, respectively. The prevalence of high myopia (<= -6.00 D) was 2.9 +/- 0.4% in the whole study population, and it was 9.9 +/- 3.0% in 17-year-olds. It was not associated with time spent outdoors (P = 0.66). CONCLUSIONS. Even in Western China, prevalence of myopia in schoolchildren is high. As in East China, low and medium myopia was associated with less time spent outdoors. High myopia was not significantly associated with outdoors time. Compared with the myopia prevalence in elderly Chinese populations, the relatively high myopia prevalence in schoolchildren in China predicts a marked increase in vision-threatening high myopia in future elderly populations in China.