The band, whose hits include "I've Seen All Good People" and "Owner of a Lonely Heart," was scheduled to play Thursday night at Denver's Paramount Theatre.
Yes released a statement Thursday saying it was canceling the shows, citing "unforeseen" medical reasons, but it didn't give further details. Its Web site said a radio performance Wednesday also had been canceled.
Frontman Jon Anderson suffered a severe asthma attack last May, was diagnosed with acute respiratory failure and was ordered by doctors to rest.
Yes initially canceled their 40th anniversary tour in the summer 2008, because of the illness of its lead singer, but then decided to relaunch it with Benoit David subbing for Anderson.
The "In The Present Tour" features guitarist Steve Howe, bassist Chris Squire and drummer Alan White.