First winter climb of Everest

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. On 17 February 1980, Krzysztof Wielicki and Leszek Cichy (both Poland) successfully climb Everest (8,848 m; 29,029 ft) - with the use of bottled oxygen -, becoming the first to reach the top of the world's highest mountain in the winter season.

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.