First winter climb of Everest without supplementary oxygen

On 22 December 1987, one day after the start of the calendar winter climbing season, Ang Rita Sherpa (Nepal, b. 27 July 1948) set off from Base Camp to successfully climb Everest without the use of bottled oxygen. As of November 2018, no other climber has repeated the feat.

Ascents occurring during the calendar (or astronomical) – comprised between 21 December and 20 March, although the winter solstice may occasionally precede or follow 21 December – and the meteorological – based on annual temperature cycles and comprised between 1 December and 28 February – winter climbing seasons present the climbers with greater challenges and dangers, as they occur when conditions are more treacherous. It must be noted that, while a winter climbing permit begins on 1 December, sometimes a distinction is made between "winter expedition" and "winter summit", where the "winter climb" strictly starts and ends within the calendar winter (21 December to 21 March). Guinness World Records takes the view that it is the start of the climb that determines its season and that the date of arrival at Base Camp is not relevant.