Objective: To report the baseline prevalence of refractive error in the study population. Design: A multicenter, longitudinal, observational study of refractive error and ocular development in children from 4 ethnic groups. Patients and Methods: The study population included 2523 children (534 African American, 491 Asian, 463 Hispanic, and 1035 white) in grades 1 to 8 (age, 5-17 years). Myopia was defined as -0.75 diopters (D) or more and hyperopia as +1.25 D or more in each principal meridian, and astigmatism was defined as at least a 1.00-D difference between the 2 principal meridians (cycloplegic autorefraction). Results: Overall, 9.2% of the children were myopic, 12.8% were hyperopic, and 28.4% were astigmatic. There were significant differences in the refractive error prevalences as a function of ethnicity (χ2, P<.001), even after controlling for age and sex (polychotomous logistic regression, P<.001). For myopia, Asians had the highest prevalence (18.5%), followed by Hispanics (13.2%). Whites had the lowest prevalence of myopia (4.4%), which was not significantly different from African Americans (6.6%). For hyperopia, whites had the highest prevalence (19.3%), followed by Hispanics (12.7%). Asians had the lowest prevalence of hyperopia (6.3%) and were not significantly different from African Americans (6.4%). For astigmatism, Asians and Hispanics had the highest prevalences (33.6% and 36.9%, respectively) and did not differ from each other (P = .17). African Americans had the lowest prevalence of astigmatism (20.0%), followed by whites (26.4%). Conclusion: There were significant differences in the prevalence of refractive errors among ethnic groups, even after controlling for age and sex (P<.001).