Abstract Transcranial pulsed Doppler (TCD) measurement of blood flow velocity in the middle cerebral artery was performed in 76 healthy children and adolescents (age 2–19 years), to obtain normative reference data, both at rest and during hyperventilation (from 10 years on). The Mean Flow Velocity (MFV) decreased with increasing age. Girls of 10 years or older showed a tendency for higher MFV values than boys of the same age. In combination with a previous study, this suggests that females in their reproductive years have higher maximal MFV values than males. The MFV values, during hyperventilation, were higher in girls than in boys. This gender difference, as in adults, disappeared gradually at lower levels of pCO 2. At the lowest pCO 2 levels, systolic minus diastolic blood flow velocity was more sensitive to vascular changes than MFV. With TCD measurements, age, sex, and pCO 2 have to be taken into account, for a correct interpretation of the data obtained.