PURPOSE: To compare computed tomographic (CT) angiography and magnetic resonance (MR) angiography with intraarterial digital subtraction angiography (DSA) in the detection of intracranial aneurysms. MATERIALS AND METHODS: One hundred forty-two patients underwent intraarterial DSA to detect aneurysms. CT angiography, three-dimensional time-df-flight angiography, and intraarterial DSA were performed contemporaneously. Film hard-copy images and maximum intensity projection reconstructions of the CT angiograms and MR angiograms were reviewed at different times. RESULTS: The accuracy per patient for the best observer was 0.87 at CT angiog- and 0.85 at MR angiography. The accuracy per aneurysm for the best was 0.73 at CT angiography and 0.67 at MR angiography. Differences between readers and modalities were not significant. Interobserver agreement was good: K value of 0.73 for CT angiography and of 0.74 for MR angiography. The sensitivity fbr detection of aneurysms smatter than 5 mm was 0.57 for Cf angiography and 0.35 for MR angiography compared with 0.94 and 0.86, respectively, for of aneurysms 5 mm or larger. The accuracy of both CT angiography and angiography was lower for detection of internal carotid artery aneurysms compared with that at other sites. With low observer confidence, the likelihood of correct interpretation was significantly poorer. CONCLUSION: CT angiography and MR angiography have limited sensitivity in the detection of small aneurysms but good interobserver agreement. There is no significant difference in diagnostic performance between the noninvasive modalities.