&NA;Overwhelming and confusing data regarding the natural history of arteriovenous malformations can confound physicians attempting to advise patients whether surgery of unruptured arteriovenous malformations is indicated. Decision analysis is a new mathematical tool that allows physicians to compare options in such patients. With the use of a simple office computer, a software program was devised to compare surgical versus conservative options in a hypothetical 25‐year‐old man. The computer model weights the important considerations of patient age, mortality and morbidity rates of the physician performing the surgery, rebleeding from the arteriovenous malformation, and patient desires, using the Markov process. When mortality and morbidity rates are reasonable, the mathematical process supports surgical intervention in the hypothetical patient. Patient guidelines for older patients and future plans for the model using grading systems are discussed. (Neurosurgery24:129‐135, 1989)