CHAMONIX, France — After 20 hours of climbing alone, navigating an 8,000-foot ice wall and surviving an avalanche that nearly knocked him off the mountain, Ueli Steck of Switzerland reached the summit of the south face of Nepal’s 26,545-foot Annapurna last Oct. 9. Eight hours later, he walked into the base camp.

In doing so, he became the first person to complete a solo climb up Annapurna’s main south face, perhaps the most technically challenging climb in the world, and notched one of the most impressive conquests in the history of mountaineering.

However, the challenge didn’t end when Steck returned to base camp. After overcoming one of the most difficult feats in his sport, Steck had to overcome doubters, who claimed that he had no proof of his climb. Steck didn’t have a photo of the summit; his altimeter had broken during his ascent; and he hadn’t used a G.P.S. tracker, all of which are accepted means of documenting such a climb. All the climbing world had for proof was Steck’s word.

Despite the controversy, last Saturday evening in Courmayeur, Italy, Steck, 37, was awarded the Piolet d’Or, mountaineering’s highest accolade, which honors the most impressive mountain climbs of the previous year. Ian Welsted, 42, and Raphael Slawinski, 47, of Canada, also won the award for their first ascent of K6 West in Pakistan.