Thorong La is the highest point on the Annapurna Circuit, a 300 km (190 mi) trek around the Annapurna mountain range. The pass is high enough to cause Acute Mountain Sickness (AMS) in trekkers who have not acclimatised to the altitude. While it is possible to cross Thorung La from Manang to Muktinath in one day, the doctors of the Himalayan Rescue Association (http://www.himalayanrescue.org/) post in Manang recommend that trekkers spend five nights between their arrival in Manang and the crossing, although two or three nights are usually enough.
The safest seasons with a clear weather window for crossing the pass is between March and April and between October and November. Attempting to cross the Thorung La in winter is dangerous due to avalanches, the risk of frostbite and the chances of losing one's way in the snow.
Most tourists cross the pass from east to west (Manang to Muktinath and Ranipauwa), which is the easiest and safest direction. Before the pass, trekkers can spend the night either in Thorung Phedi (at 4420 m) or at Thorong High Camp (4800 m), meaning that they will have to climb a maximum of 1000 m and descend about 1,600 m (5,200 ft). The way from Muktinath does not offer opportunities for altitude acclimatisation, with the last spot where it is possible to spend the night being at 3700 m (Ranipauwa, all year round) or at 4200 m (Muktinath Pedhi with a very basic seasonal lodge), meaning that a trekker going from west to east will have to ascend 1700 m or 1200 m and descend at least 600 m in one day.
If crossing the pass in October/November, an early start (at least a few hours before sunrise) in going over the pass is recommended as strong winds typically begin a few hours after sunrise.