Objectives: Central arterial pulse wave augmentation, quantified by the augmentation index (AIx), is a key marker of arterial health, an important contributor to cardiac afterload and is significantly greater in older women than men. We measured carotid AIx in 8-year-old children to examine the influences of sex, height and arterial stiffness on central arterial pulse wave augmentation Methods: Four hundred and five children (age 8.0 ± 0.1 years, 49% girls) had anthropometry, brachial systolic and diastolic blood pressure, heart rate and carotid artery pressure waveforms (by applanation tonometry), diastolic diameter and distensibility assessed. Results: Carotid AIx was significantly higher in girls than boys (-11.7 ± 8.1 versus-16.5 ± 9.3%, respectively, P < 0.001). Boys and girls had similar height (129 ± 6 versus 128 ± 6 cm), systolic blood pressure (100 ± 7 versus 101 ± 7 mmHg), diastolic blood pressure (59 ± 6 versus 60 ± 5 mmHg) and heart rate (80 ± 10 versus 82 ± 10 bpm). Carotid diastolic diameter was smaller in girls than boys (0.45 ± 0.03 versus 0.47 ± 0.04 cm, P < 0.001). The sex difference in AIx remained significant after adjustment for height, heart rate, blood pressure, diastolic diameter and birth weight. The time to the onset of the reflected wave was shorter in girls (155 ± 19 versus 163 ± 18 ms, P < 0.001). Girls had greater carotid artery distensibility (6.2 ± 1.8 versus 5.8 ± 1.5% per 10 mmHg, P = 0.016), suggesting lower regional carotid artery stiffness. Conclusion: Greater pulse wave augmentation in prepubertal girls results from earlier wave reflection and is independent of height, carotid artery diameter and stiffness. When combined with age-related changes in arterial compliance, this may contribute to adverse cardiovascular outcomes in older women.