From their press release:

Legendary rock band Yes announced today that the group will unfortunately be canceling their 2008 40th Anniversary Tour. The 26-city tour was scheduled to kick off in Quebec next month and run through the summer.

Said Jon Anderson, “In the wake of my recent respiratory attack, doctors have advised me to spend the coming months resting and recovering. Unfortunately, this means I won’t be able to tour with Yes this summer as originally planned. I’d like everyone to know how deeply disappointed I am by this turn of events. I was looking forward to celebrating our music with the amazing family of Yes fans once again; but as we all know, health must come before anything else. Wishing you all the very best…”

Yes was supposed to play WaMu Theater on August 15th. Bummer.