PURPOSE. We describe changes in choroidal thickness from age 11 to 16 years and its association with ocular biometrics and body development. METHOD. In this longitudinal, population-based observational study, choroidal thickness was measured subfoveally and 1- and 3-mm temporal thereof using enhanced depth imaging spectral domain optical coherence tomography. Analyses were stratified by sex and adjusted for age and the time of day that the scan was performed. RESULTS. The study included 687 participants (304 boys). Median (interquartile range [IQR]) age was 11.5 (0.6) years at baseline and 16.6 (0.3) years at follow-up. Mean increase in choroidal thickness was 33, 27, and 11 lm at the three respective locations. The subfoveal choroid thickened less in eyes whose axial length increased more (boys, b ¼ 85 lm/mm; 95% confidence interval [CI], 104 to 66, P < 0.0001; girls, b ¼ 105 lm/mm; 95% CI, 121 to 89, P < 0.0001) and in eyes with a more negative refractive development (boys, 11 lm/diopters [D]; 95% CI, 4.0 to 18, P ¼ 0.0022; girls, 22 lm/D; 95% CI, 16 to 27, P < 0.0001). Subfoveal choroidal thickness increased less in girls who underwent early puberty (Tanner stage 4 vs. 1; 39 lm’ 95% CI, 72 to 5.9, P ¼ 0.021) and who had a longer baseline axial length (b ¼ 8.6 lm/mm; 95% CI, 15 to 2.7, P ¼ 0.0043), and more in girls who grew taller (b ¼ 0.9 lm/cm; 95% CI, 0.1 to 1.7, P ¼ 0.026). CONCLUSIONS. The choroid increased in thickness from age 11 to 16 years. The increase was greater in girls with later sexual maturation and smaller in eyes that added more axial length and had a relatively negative refractive development. Keywords: choroidal thickness changes, longitudinal study, cohort study, axial eye growth