Objective. To investigate the determinants of aortic pressure waveform morphology in the thoracoabdominal aorta with specific reference to features of potential prognostic value for cardiovascular disease. In particular we aimed to determine the location of major pressure wave reflection sites within the aorta. Methods and Results. Aortic pressure waveforms were acquired using 2F Millar Mikro-tip® catheter transducers in 40 subjects (26 male), and repeated in 10, at 5 pre-determined points within the aorta: aortic root, transverse arch, at the levels of the diaphragm, renal arteries and aortic bifurcation. Waveforms were analysed for augmentation index (AI), time to inflection point (Ti) and pressure parameters. AI decreased progressively between the aortic root and bifurcation (P < 0.001), and Ti increased (P < 0.01). There was the expected progressive peripheral amplification of systolic and pulse pressures and fall in time to peak pressure (all P < 0.001). There was no difference on repeat pullback, or between genders. Conclusion. These data are at variance with the concept that central AI results solely from pressure wave reflection, when Ti would be expected to decrease and AI increase with distal progression. Pressure wave propagation phenomena may contribute, and the potential role of frequency dispersion merits investigation.