The cross-sectional area of the common carotid artery bulb was measured using a 5 MHz pulse wave Doppler probe in a patient undergoing general anaesthesia using a laryngeal mask airway (LMA). A simultaneous measurement of blood velocity was performed to allow determination of the blood flow. Following inflation of the cuff on the LMA, the cross-sectional area of the right carotid artery bulb decreased from 1.09 to 0.89 cm2, flow velocity increased 120 to 176 cm s-1 and the blood flow increased from 130.8 to 156.6 cm3 s-1. On the left the cross-sectional area decreased from 1.16 to 1.13 cm2, the velocity increased 136 to 151 cm s-1 and the blood flow increased from 157.8 to 170.6 cm3 s-1. While a reduction in cross-sectional area was observed in the carotid bulb in this patient, this was accompanied by an increase in the velocity and a consequent increase in blood flow. In patients with atheromatous disease involving the carotid arteries this decrease in cross-sectional area may prove clinically significant. The use of the LMA may not be suitable for this population.