Methods for measuring the ventilatory response to hypoxia (HVR) are reviewed. The criteria for success as a high altitude mountaineer are defined as freedom from acute mountain sickness (AMS) and ability to perform well at extreme altitude. The evidence for a brisk HVR being protective against AMS and associated with successful high altitude performance is reviewed. The contrary evidence of blunted HVR in high altitude residence and some elite climbers is discussed. The effect of a brisk HVR in producing periodic breathing when asleep at altitude is noted. It seems that there is an optimum HVR for different circumstances and peoples. A brisk HVR is a benefit in lowlanders going to altitude for the first time whereas a blunted HVR is appropriate for high altitude residents and possibly for very experienced elite climbers.