Epistaxis is the most frequent reason for adult emergency admission to otolaryngology units in the United Kingdom. Despite it's prevalence the aetiology of epistaxis is poorly understood and most cases are idiopathic. In addition management of the condition involves numerous untested treatment strategies backed by a literature consisting almost entirely of case reports, anecdote and review articles. Few aetiological factors or treatment strategies have been the subject of prospective research. This thesis used a series of prospective research studies to examine aspects of the aetiology and management of adult idiopathic epistaxis. Data was prospectively collected on admissions to the otolaryngology department of Glasgow Royal Infirmary. All clinical work was performed on a defined population of adult (20 years or older), idiopathic epistaxis patients identified by exclusion of cases with a known cause for their bleeding (trauma, surgery, tumours, anticoagulant medication, blood dyscrasia, haemophillia, hereditary haemorrhagic telangiectasia). Overall Conclusions: The septal arteries have been shown to be the main site of adult posterior epistaxis, casting doubt on the importance of Woodruffs plexus. Important aetiological associations between alcohol, NSAID and epistaxis have been confirmed and a possible haemostatic mechanism for the effect of alcohol has been demonstrated. Nasal septal deviations have not been confirmed as important in the causation of adult idiopathic epistaxis. Deficiencies in first aid management by hospital staff have been identified and flaws in the design of epistaxis balloon catheters highlighted. Thus, non-specialist treatment of epistaxis may be improved by education of accident and emergency staff and improved design of nasal balloon catheters. The theoretical ideal of direct endoscopic haemostasis in posterior epistaxis has been shown to be clinically feasible, efficacious and worthy of further study.