THREE PATIENTS WITH transient ischemic attacks (TIAs), a stenotic or ulcerating carotid lesion, and an unruptured aneurysm are discussed. Decision analysis is used in comparing treatment strategies for each patient: clipping of the aneurysm, endarterectomy, or both, with or without platelet aggregation inhibitors. Bayesian sensitivity analysis with Monte Carlo simulation is used to estimate 95% confidence limits for the difference in discounted quality-adjusted life expectancy between the treatment strategies. Platelet-inhibiting therapy is indicated for all three patients, despite the increased risk of complications from subarachnoid hemorrhage. Carotid endarterectomy cannot be recommended for any of the three patients. With regard to aneurysm surgery, a toss-up exists in one patient; in another, the aneurysm should be clipped; and in one, the decision depends on the probability that the TIAs originate from the aneurysm. Guidelines for the management of similar patients are given. For patients with TIAs, a moderate carotid stenosis, and an intracranial aneurysm that does not seem to be related to the symptoms, neither clipping of the aneurysm nor endarterectomy can be recommended with confidence; however, when the intracranial aneurysm is just as likely to be the source of the TIAs as not, clipping is recommended up to the age of 70, when the surgical risks are moderately high.