Clinical decision analysis is applied to treatment decisions for three patients with unruptured familial intracranial arteriovenous malformations (AVMs) in association with hereditary haemorrhagic telangiectasia (HHT). The grades of the AVMs--according to Spetzler--were 1-0-0 (two patients aged 12 and 14) and 2-0-1 (one patient aged 43). The AVM in one patient (graded 1-0-0) was operated on without sequelae. In the decision analysis, life expectancy is used as an outcome measure, with and without quality of life adjustment and discounting for time preference. It is concluded that neurosurgical treatment is the optimal strategy for all three patients. Because no conclusive data are available concerning the natural history and neurosurgical treatment of unruptured AVMs, we recommend the prospective application and testing of AVM grading systems. General treatment guidelines balancing the lifetime risk of haemorrhage, risk of incomplete extirpation and surgical mortality and morbidity are given. The analysis suggests that patients with low-graded AVMs which have not bled should be treated surgically, unless they are older than 60 years and have an increased risk of incomplete extirpation.