Objectives-To determine whether combining non-invasive tests for intracranial aneurysms together would significantly improve aneurysm detection over individual tests. Methods-114 patients undergoing intraarterial digital subtraction angiography to confirm or exclude an intracranial aneurysm were also examined by CT angiography, AIR angiography, and transcranial power Doppler ultrasound. The reviewers and ultrasonographers were blinded to the angiogram. result, other imaging results and all clinical information. Results-The combination of noninvasive tests did improve diagnostic performance on a per patient basis. The combination of power Doppler and CT angiography had the greatest sensitivity for aneurysm detection (0.83; 05% confidence interval (95% CI) 0.66-0.93) and the level of agreement for this strategy with the reference angiographic standard was excellent (kappa 0.84; 95% CI 0.72-0.95). The improvement in sensitivity of adding power Doppler to CT angiography was not significant (p = 0.55) but the improvement in the level of agreement with the reference standard was substantial. However, even the most sensitive combination strategy performed poorly in the detection of small (3-5 mm.) and very small (< 3 mm.) aneurysms with a sensitivity of 0.43 (95% CI 0.23-0.66) and 0.00 (95% CI 0.00-0.31) respectively. Conclusions-The addition of transcranial power Doppler ultrasound to either CT angiography or NM angiography does improve diagnostic performance on a per patient basis but aneurysms of 5 mm or smaller can still not be reliably identified by current standard clinical non-invasive imaging modalities.