Background and Purpose— Although intracranial vascular malformations (IVMs) are the leading cause of intracerebral hemorrhage (ICH) in young adults, there has not been a cost-of-illness study on an unselected cohort. Methods— We measured the direct healthcare costs (inpatient, outpatient, intervention, and brain imaging) incurred by every adult within 3 years after their first presentation with a brain arteriovenous malformation (AVM) or cavernous malformation (CM) in a prospective, population-based study. We estimated the indirect cost of lost productivity for the whole cohort over the same period by projecting questionnaire responses from living consenting adults. Results— 369 adults (AVM=229 [62%], CM=140 [38%]) incurred healthcare costs of £5.96 million over 3 years, of which AVMs accounted for 90%, inpatient care accounted for 75%, and the first year of care accounted for 69%. Median 3-year healthcare costs were statistically significantly higher for adults presenting with ICH, aged <65 years, receiving interventional treatment, and adults with AVMs rather than CMs (£15 784 versus £1385, P <0.0005). Healthcare costs diminished with increasing AVM nidus size ( P =0.005). Mean 3-year costs of lost productivity per questionnaire respondent (n=145) were £17 111 for AVMs and £6752 for CMs ( P =0.1), and the projected 3-year cost of lost productivity for all 369 adults was £8.7 million. Conclusions— The costs of healthcare and lost productivity attributable to IVMs are considerable, and highest in those aged <65 years, presenting with ICH, receiving interventional treatment, and harboring AVMs rather than CMs. Long-term studies of the cost-effectiveness of interventional treatment are needed.