This article gives the probable location within 65 km of the Big Headache Mountain where mountain sickness was first reported by Too Kin, a Chinese official, in 37-32 B.C. We believe that traveling over the western edge of the Himalayan Karakoram Range or in the Pamirs caused the major difficulties, probably when travelers crossed the Kilik Pass at an altitude of 4827 m or 15837 ft or within 60 km of this pass and at an altitude of at least 4500 m or 14750 ft. We theorize that the route Too Kin described is from Kashi, an important center in Sinkiang or Chinese Turkestan, to Kabul in Afghanistan. This particular route has two other altitude maxima; one at the Ulagh Rabat Pass in Sinkiang about 15 km west of the Muztagata peak where the elevation is 4250 m or 14000 ft, and the other at the Shandur Pass over the Hindu Kush in Pakistan where the elevation is 3734 m or 12250 ft.