Scottish Intracranial Vascular Malformation Study was the first prospective, population-based study of the major types of intracranial vascular malformations; arteriovenous, cavernous and venous malformations including dural fistulae and carotid-cavernous fistulae. It was based in Scotland and designed in 1998 by my supervisor Professor Charles Warlow and the first Research Fellow Dr Rustam Al-Shahi supported by the SIVMS steering committee (www.saivms.scot.nhs.uk). Recruitment and follow-up began in January 1999. Recruitment and follow-up of all vascular malformation types was done by Dr Al-Shahi until March 2002 and this role then transferred to me in April 2002 until I left in August 2004. The main duties of the Research Fellow were to collect and review all the clinical material of cases notified to SIVMS and arbitrate with the relevant expertise where there was doubt whether the case met the criteria for inclusion in SIVMS. Apart from my clinical responsibilities in recruitment and follow-up, the post also involved supervision of the part-time study administrator and also weekly meetings with the study programmer. I was also responsible for convening and presenting updates of the study progress weekly to my supervisor Professor Charles Warlow, biannually to the Study steering committee meetings, and annually to my funding body, the Stroke Association. This Research Fellowship also allowed me to gain an appreciation of the efforts needed to sustain collaborators’ interest in a long running study and I made presentations to improve the profile of the study on the national and international stage. For my duration as the SIVMS Research Fellow, I recruited and followed-up all types of newly diagnosed intracranial vascular malformations (IVMs). This thesis, however, is based solely on the incident intracranial cavernous malformations (ICMs) recruited to the study by both Dr Al-Shahi and myself between January 1999 and December 2003. The follow-up data in this thesis were that available to me on August 31st 2004. The data cleaning and the analysis for this thesis has been performed by me alone under the supervision of Professor Warlow. Although the core study design was well-established and tested prior to my involvement with SIVMS, I did divise new studies such as the Sensitivity and Specificity of MRI in the diagnosis of intracranial CMs. This cavernoma imaging study was a separate study designed, executed and analysed by myself, a medical student Sue Liong, the Cavernoma Imaging Study Group [appendix 1] with guidance from Professor Warlow, Dr Al-Shahi, Dr Andrew Farrall (consultant neuroradiologist) and Dr Steff Lewis (Medical Statistician). Computing support was provided by Aidan Hutchison (SIVMS programmer).