['To examine the association between the longitudinal changes of axial length (AL) and height in Chinese children.', 'The study participants were recruited from the Guangzhou Twin Registry. AL and height were measured every year from 2006 to 2008. AL was measured using partial coherence laser interferometry. Height was measured with the participants standing without shoes. Bivariate correlation coefficients and a multivariate generalized regression model were used to calculate the association between the changes of AL and height. Data from the first-born twins were selected to present the results: The right eye was arbitrarily selected to represent AL of the specific individual.', 'Mean annual increases of AL and height were 0.22 (SD, 0.17) mm and 3.93 (SD, 3.02) cm, respectively. Correlations between AL and height were 0.47 (95% CI, 0.40-0.52) in 2006. The correlation between AL at 2006 and height at 2008 was 0.44 (95% CI, 0.37-0.51); the correlation between AL at 2008 and height at 2006 was 0.38 (95% CI, 0.32-0.45). These cross-trait cross-time correlation coefficients remained statistically significant after adjusting for age and sex. Plotting the changes of AL and height suggested that the changes of AL and height with age were concomitant; greater changes were observed in younger children.'] Are longitudinal changes of axial length and height associated and concomitant in children?