Cardiovascular disease is the greatest cause of death globally and places a major burden on healthcare systems. Aortic dissection and aneurysm have some of the most catastrophic consequences when left untreated. Increasingly clinicians are seeking improved clinical tools to quantify risk. In this thesis we apply computational fluid dynamics to patient-specific geometries to observe haemodynamics. We develop computational models for iliac aneurysm and type B aortic dissection and through simulation on a supercomputer, apply these methods to large clinical datasets. The results are then used to develop a new morphological categorisation for each disease which we show predicts clinical outcomes.