The main aim of this study is to define the clinical criteria which must be considered in order to come to an adequate decision whether a patient with intracranial arteriovenous malformation (AVM) should be operated upon or treated conservatively. A special method was used to reduce the effects of selection. This method made it possible to evaluate the therapeutic efficacy of conservative treatment versus surgery. The method implies that patients with equal combinations of variables (risk profiles) were compared in the two treatment lines. The variables building up the risk-profile pattern...