PURPOSE: To describe the relationships of retinal vascular caliber to optic disc diameter in children. METHODS: A school-based cross-sectional study of 746 children aged 7 to 9 years who participated in the Singapore Cohort Study of the Risk Factors for Myopia. Digital retinal photographs of both eyes were taken in 2001 and graded for retinal vascular caliber, vertical optic disc diameter, and vertical cup-to-disc ratio (CDR) according to standardized protocols. All measurements in pixels were analyzed after correction of the magnification. RESULTS: In this study population, the mean retinal arteriolar caliber (SD) was 5.95 (0.51) pixels, retinal venular caliber was 8.58 (0.69) pixels, vertical disc diameter was 73.02 (7.48) pixels, and vertical CDR was 0.34 (0.09). In multiple linear regression analysis with adjustment for age, gender, ethnicity, body mass index, and birth weight, arteriolar caliber decreased by 0.011 pixel (P < 0.001) and venular caliber decreased by 0.016 pixel (P < 0.001), for each pixel decrease in vertical optic disc diameter. The associations remained similar and statistically significant with further adjustment for blood pressure. Vertical CDR was not related to retinal vascular caliber. CONCLUSIONS: In this population of generally healthy children, smaller vertical optic disc diameter was associated with narrower retinal arteriolar and venular calibers. The findings of this study, in conjunction with studies in adults, suggest anatomic relationships between the optic disc and retinal vasculature that may provide additional insights into the vascular etiology of glaucomatous and nonarteritic anterior ischemic optic neuropathy. However, because the detected differences in retinal vascular caliber were small, the clinical significance of the study findings remains uncertain.