Objective An association between birth weight and blood pressure has been reported in many studies, but the strength of this association has been disputed. Birth weight could, however, be associated with alterations in the proximal arterial tree that have little effect on blood pressure. The objective of this study was to examine the relationship between birth weight and characteristics of the proximal arterial tree determined by pulse wave analysis. Methods An optically derived digital volume pulse was used to obtain indices of pressure wave reflection (reflection index; Rl) determined by characteristics of small/ medium sized arteries and of large artery stiffness (stiffness index; SI) in healthy young adults (n = 220, 111 women, aged 16-26 years). Birth weight was obtained from maternal recall. Results Diastolic blood pressure was significantly correlated with birth weight (P < 0.001) but birth weight accounted for only 5% of the variance in diastolic blood pressure. RI was significantly correlated with birth weight in women (r = -0.33, P < 0.001) but not in men, and there was a significant interaction between birth weight and sex (P < 0.001). SI was significantly independently correlated with birth weight in both men and women (r = -0.41 and -0.49, each P < 0.0001) and birth weight accounted for 17% of the overall (men and women) variance in SI. Conclusions These results suggest a close association between birth weight and characteristics of the arterial tree proximal to resistance vessels in young adults and a sex-specific association with characteristics influencing arterial pressure wave reflection. (c) 2005 Lippincott Williams & Wilkins.