To determine ethnic differences in time-domain (Stratus) optical coherence tomography-measured macular thickness in 12-year-old children.Population-based cross-sectional study.A total of 2367 children from grade 7 (mean age 12.7 ± 0.45 years) examined during the Sydney Myopia Study during 2004-2005.Examination included determination of best corrected visual acuity. Autorefraction was performed after cycloplegia. Axial length was measured using non-contact interferometry and OCT was performed using Stratus OCT. Ethnicity was self reported by participants' parents.Macular thickness.The four largest ethnic groups were Caucasian (n = 1224), East Asian (n = 291), South Asian (n = 107) and Middle Eastern (n = 146). The greatest ethnic differences were found at the central macula, which was significantly thicker in Caucasian compared with East Asian, South Asian and Middle Eastern children (mean differences 9.0 µm, 12.1 µm and 6.5 µm, respectively; all P < 0.0001). The average inner macula was significantly thicker in Caucasian than East Asian and South Asian children (P = 0.005 and P < 0.0001, respectively). The average outer macula was significantly thicker in Caucasian than Middle Eastern and South Asian children (P = 0.03 and P < 0.0001, respectively).Macular parameters were found to vary by ethnicity in 12-year-old children. Caucasian children had the thickest macular parameters and South Asian children had the thinnest. The greatest differences were found in the central macula.