Transcranial colour-coded sonography (TCCS) is a new development in noninvasive cerebral vascular imaging. We studied 5 patients with known intracranial aneurysms and 12 patients with arteriovenous malformations (AVM). We were unable to image any of the aneurysms (all 5 mm or less in diameter) using colour flow ultrasound. Similarly, pulsed wave Doppler interrogation failed to reveal any flow disturbances. Nine out of 12 AVMs were successfully visualised as serpiginous structures and the principal feeder vessels were identified in 11 cases. Blood flow velocities in the feeder vessels were elevated compared with the same vessel contralaterally (median [cm/s]; peak systolic 227 vs. 89, P = 0.001; mean 178 vs. 57, P = 0.001; end diastolic 138 vs. 37, P < 0.0005). Pulsatility indices (PI) and resistance indices (RI) in the feeder vessels were reduced relative to the same vessel contralaterally (median PI 0.46 vs. 0.94, P < 0.0005; median RI 0.37 vs. 0.59, P < 0.0005). At present, TCCS appears of little value in the diagnosis of intracranial aneurysms, but it shows promise for the imaging of AVMs and their haemodynamic study.