The present invention provides a ventilated casing for an electronic device. The ventilated casing includes a housing which has a ventilation inlet and a ventilation outlet. The ventilated casing also includes a high speed fan for moving air from the ventilation inlet to the ventilation outlet to dissipate heat that in use is generated by electronic components positioned in the housing. The fan has a blade, a motor and an air guiding portion positioned near the blade. The air guiding portion has a first mode resonance frequency that is greater than the rotational frequency of the fan.