Clinical decision analysis is applied to the treatment decisions for four patients with unruptured familial aneurysms. The surgical treatment was uneventful in all patients except one with mild mixed aphasia and facial weakness postoperatively; these deficits disappeared in less than 2 years. In the decision analysis, discounted Quality Adjusted Life Years are used as an outcome measure. Probability estimates are extracted from the literature when available. It is concluded that the decision to treat the aneurysm neurosurgically in three of the four patients was correct. In two of these three patients, the decision cannot be altered by plausible changes in estimated data. For the third patient, only the combination of a low probability of rupture, a high surgical mortality and morbidity, and high discount favors conservative treatment. In the fourth patient, a toss-up situation exists. More knowledge of the probability of rupture, the probability of the development of other aneurysms, and the results of operation on intact intracranial aneurysms would have made the analysis more accurate. Clinical research should address these issues.