Spontaneous dissection of the internal carotid artery (ICA) is an unusual finding. We present an analysis of five patients (aged 40-60 years) with ICA dissections, describing the various flow patterns detected on colour Doppler ultrasound. Particular attention was paid to the presence of a dual lumen, the direction of flow in the false lumen and the velocity/spectral broadening of the Doppler trace obtained from the true and false lumens. Four different patterns were observed. Narrowing of the true lumen by the false lumen thrombus was seen in two cases with a low velocity Doppler waveform; three cases had a patent false lumen ("double lumen" pattern); the direction of flow in the patent false lumen varied from being (i) forward, (ii) reversed and (iii) bidirectional. The flow dynamics in carotid dissections are complex and are primarily dependent upon the presence of thrombus within the false lumen, the entry and exit flaps if the false lumen is patent, the motion of the flap wall and the extent of the dissection. They illustrate the diverse nature of the disease and Doppler ultrasound plays an important role in the imaging of ICA dissections.